My understanding is that mutating built in prototypes is very bad. Not just for interop reasons, but because doing so really hinders many optimizations javascript engines perform.
Adding methods to prototypes is effectively free. The only time mutating a builtin prototype has negative consequences is when you replace a builtin function with your own thing. All javascript engines (that I'm aware of) JIT at the method level so there's not really a performance impact modifying a prototype.
There is an issue you need to be aware , be careful if you hide the fact that this collection is "live". I mean this part from the docs
>An HTMLCollection in the HTML DOM is live; it is automatically updated when the underlying document is changed. For this reason it is a good idea to make a copy (eg. using Array.from) to iterate over if adding, moving, or removing nodes.
So you need something that will also be efficient and correct, not a 5 minutes implementation.
Same issue applies if you mutate array you're iterating over during iteration using those Array.prototype functions. This is just a general issue with any data structure.
