That's too controversial to imagine with a majority of Scarborough Councillors, MPPs and MPs that all previously had campaigned and won their respective elections on advancing the subway extension cause. More likely they'll defer til the 2023 Federal election to make a final decision, which will likely be a subway.
SELRT is more of that parochial line of thinking that one mode of transit suits all when frankly it doesn't. East of Midland could easily be operated with mere express buses while boosting the Don Mills to Scarborough Centre piece which a) has to be underground anyway to Victoria Park, b) can be completely operated elevated southeast of Agincourt saving costs and c) can easily be extended to Malvern Town Centre via the same alignment as the SRT via Centennial College. These are big advantages the subway has that the LRT in a straight line to Meadowvale never will have.
When Richmond Hill, Vaughan, UTSC, the Airport and the downtown core all get new grade separated transit within this same timeframe; it will only look petty and vindictive not to pursue a northern crosstown line.