You are the one who first made baseless claims that things would have no cost because they are already there, just leave them and implement a new one on the side

As a software developer, I can come up with a long list of things that cause extra effort, even if you just leave some stuff in rather than replace it with a new implementation. Here is a random non-comprehensive list that might cause extra work, but I'm not an insider, so I don't speficially know and it also varies case by case:
* You must now test both implementation when something changes
* You must support an UI that allows selecting which implementation you wish to use plus localization for that
* You must support the mechanics of switching between implementations
* Since there are two implementations and everything that interacts with this thing, will have to work with both implementations
* Users will have to make a choice which implementations they use (this is not always a positive thing)
* System/code complexity is higher, leading to higher cognitive load for designers/developers and increasing chance of bugs
* All future changes will need to be made for both implementations

I'm not saying there shouldn't be options or that we shouldn't suggest ones, but you must understand that each option will have a cost. None of them are free like some seem to think and blame Larian for being lazy/evil/mean/incompetent when they don't implement them