[4] In October 2013, the TTC announced plans to give the lines official numbers to help riders and visitors navigate the system.

[8] The plan was approved by Metropolitan Toronto, but funding was delayed by the provincial government of David Peterson's Liberal Party.

In 1993, the governing New Democratic Party (NDP) under Bob Rae proposed provincial funding for four subway/LRT projects for the TTC.

Included in these four proposals were plans to build new subway lines along Eglinton and Sheppard Avenues and work was begun on both projects.

[11] David L. Gunn, who was general manager of the TTC, opposed the Sheppard line, saying that it "made no sense to build an expensive new subway when the existing system was strapped for cash to make basic repairs" and "if the city wanted to expand transit, it would be better to do it downtown, easing congestion in the busiest parts of the system".

[15][16] From its opening in 2002 to 2014, the Sheppard line spurred over $1 billion of construction of new housing,[17] including several high-rise condominium towers, along its route as transit-oriented developments.

[11] The Daniels Corporation built a six-tower condominium development, called NY Towers, north of Highway 401 between Bayview and Bessarion stations; Arc Condominiums on the northeast corner of Bayview Avenue and Sheppard Avenue; and terraced condos just east of their NY Towers.

The following table shows the typical number of customer trips made on the Sheppard subway on an average weekday.

[31] Similarly, as a result of financial pressures brought on by the COVID-19 pandemic in Toronto, Mayor John Tory announced in 2020 that the entire line would be shut down without financial support from upper levels of government,[32] though funding was eventually secured to allow the line to remain open.

"[33] Councillor Josh Colle, who chaired the TTC from 2014 to 2018, said in May 2015 that, given the existing Sheppard subway's performance, he could rationalize spending more money to expand it east from Don Mills or west from Sheppard–Yonge, but not both.

[34] According to the Metro commuter newspaper, between the opening of the Sheppard line in November 2002 and December 2014, there was over $1 billion in development along that corridor, much of it in the vicinity of Bayview, Bessarion and Don Mills stations.

The area surrounding Don Mills station has a density suitable for a subway at 10,182 people per square kilometre (26,370 people/sq mi).

[37] In 2019, the provincial government under Premier Doug Ford announced it supported an eastern extension of the line as a longer-term project.

The maximum capacity of the subway option was about 30,000 riders per hour, approximately the load the Yonge portion of Line 1 carried in the morning rush.

[34] In April 2019, the provincial government under Premier Doug Ford announced that it supported an eastward extension of Line 4 but included no promise of funding nor a proposed target date for completion.

The approval of the Spadina subway extension to the Vaughan Metropolitan Centre in York Region renewed interest in this phase, as a subway connection between Sheppard West and Sheppard–Yonge stations would significantly lower commuting times for York University students, as well as commuters travelling to and from Vaughan Metropolitan Centre.

[47] In December 2013, this extension was listed as being under consideration as an "unfunded future rapid transit project" in the City of Toronto's "Feeling Congested?"

Under this plan, the Sheppard East subway extension had been replaced by a light rail line running from Don Mills Station along Sheppard Avenue East to Meadowvale Road, where it would have met the northern terminus of an extended Line 3 Scarborough.

Massive redevelopment along the route would be needed to generate these funds, as the then-current population density and projected ridership was too low to support the cost of the expansion by itself.

[53][54] In 2011, Metrolinx estimated that the westward extension to Sheppard West would be 5.45 km (3.39 mi) long, add two stations, and cost $1.48 billion.

[55] Gordon Chong, head of the TTC agency tasked with analyzing the new subway plans at the time, said it was possible that no new transit development would occur along Sheppard Avenue.

In the meeting, council voted to build the Eglinton project according to the original Transit City plan (partly underground and partly at grade), build an at-grade Finch West LRT, and to appoint a panel to recommend whether to pursue the eastward extension of the Sheppard subway or construct the Sheppard East LRT instead.

[59] On April 26 of that year, the motion to build the LRT was announced by the Minister of Transportation after being approved unanimously by Metrolinx.

[61] During the 2014 Toronto mayoral election, incumbent mayor Rob Ford (and his brother Doug Ford, after the prior's withdrawal) were the only major candidates who supported completing Line 4 Sheppard east to McCowan Road (phase-one project) and west to Sheppard West station (phase-two project).

[62] John Tory, who won the election, did not include anything on the Sheppard corridor in his maps; instead, he favoured SmartTrack, a proposal to enhance GO Transit rail service with the city of Toronto.

[37] In July 2016, Toronto City Council approved a one-stop subway extension on Line 2 Bloor–Danforth to Scarborough Centre station.

Following Ford's re-election as premier of Ontario, the Ontario Fall Economic Statement in 2022 recommitted the government to the eastward extension by confirming planning work had continued for the Sheppard subway extension, which would extend Line 4 from its existing terminus at Don Mills station to McCowan Road.

[65] On June 8, 2023, Associate Minister of Transportation Stan Cho announced that he and Minister of Transportation Caroline Mulroney had given official direction to agency officials to prepare an initial business case to extend Line 4 eastwards to the terminus station of the Scarborough subway extension (located at McCowan Road and Sheppard Avenue East) and to explore the potential for extending the line westwards to Sheppard West station.

[69] The 385 Sheppard East Blue Night bus route provides late-night service when the subway is not in operation with the frequency of 30 minutes.