With LRT track in place along Hurontario there's no physical reason why the Eglinton/Transitway LRT service would have to actually terminate at Square One. It could just as easily terminate at Cooksville or Port Credit.
As for having it as a super long line, there's the opportunity to run multiple routes on the same track. One from Port Credit to Pearson (a much needed direct airport connection from the Lakeshore West line for passengers coming from the west), one from MCC to Science Centre (bypassing the airport), one from Pearson to Kennedy, and one from Mount Dennis to Morningside. The busiest sections would have overlapping lines leading to a higher frequency, while the lower demand sections would have a single route on them.