That is a little past the basic 531 principle for assistance work but again if you treat it as main work it can work.
When doing single leg for assistance I usually just get the rep total for the day based on how I feel. If I’m still sore from the last squat session I might do the 50 with bodyweight only in as few sets as possible. If feeling good, I might grab some DBs or chains and after 1 set with BW I would do the rest of the sets with increasing weight until I hit it, or with the same weight with near max reps each set.
For main work, probably your approach would work better because it sets more goals and challenges, so psychologically it can be more stimulating as well. Depending on your approach, you can scale it that way, you can even add a 531ish twist to it, say one week you do 20s then 25s, then 30s the third week, and you kind of wave it like that in 3 week cycles, really just to make it more fun or interesting.
Going with your example, the way I can see that working is if you have limited number of sets, because if I have enough patience and energy, I can grab a pair of 80s or 100s (never actually went beyond 88lbs total weight on BSS) and BSS my way to 50, 1 rep per set. So say you have a rep goal of hitting in this case 100. Set a goal of doing it with X weight, in I don’t know, 5 sets. Then you have multi layer form of progression, you can reduce sets, increase weight, if you want you can reduce rest time, increase tempo, add pauses, a million ways to measure progress. Once you hit 100 per leg with X weight in your chosen number of sets, add weight, slow tempo, reduce sets, you get the idea. And on top of that you can still add some kind of a 531 twist I mentioned so you don’t max out every week.
If you are creative you can come up with all kinds of ways to make this work, and even fun. Not to mention if your injury recovers after surgery and you are able to squat again without causing yourself damage or pain, your weak side will be almost non existant.
Again, these are all just ideas and general suggestions, consult with your PT/doctor and listen to your body.