Low floor trains are more accessible as long as stations are on curbs. You do not need retractable ramps if the stations are designed properly. Who builds new LRT today requiring riders to step up from the street? This is not 1920 anymore.
High floor trains require more extensive stations and ramps for those using mobility devices. Low floor gives more direct access to the trains without following extended ramps.
On the topic of ramps and boarding height, (Preface I am not exactly an expert on these things)
Line 6 Finch West already has a variety of ramps for its stops because LRVs cannot be level-boarded from curb height. The ramps range from about 7m to 20m (wow! at Duncanwoods) based on aerial. Based on my VERY ROUGH assessment, i'd wager the stops have about 13m on average, and none of the shorter ramps seem to have been due to any restraints that would have made it problematic if the ramp was longer.
For reference, at maximum permissible ramp grade of 1:12, the ramp to the TOR boarding of 355mm for LRVs is 4m, and at the lowest end at 1:20, 7m. Anything below 1:20 doesn't need a landing, so that's why the longer ramps don't have them.
If 6 was built at high floor standards a la subway with a TOR of 1105, you could either do a 1:12 ramp at 13.3m + one intermediate landing or a 1:21 ramp at 23m. So, more realistically if you did 1:12 + a landing, you'd hit about 15m overall.
I don't think this is a significant problem. I don't think there are any stops on 6FW that are technically restricted from being extended another 8 metres at the most, and some exceed this length already.
TL;DR 6FW already has ramps from 7 to 20m, a high floor vehicle (1105mm above TOR) would need minimum ~15m ramp, they would both have level boarding and accessibility, and there's not really any technical limitations at any stops that I know of that would prevent it from working.
sidenote/edit can we please stop penny-pinching about perhaps the cheapest part of this line- the length of the platforms- when literally every other part of this line has been overbuilt