The situation with public APIs is less than ideal. Many useful things can only really be accomplished by hard-coding low level stuff.
But more importantly, the conditions today are far from good for considering new APIs or expanding existing ones. We're in the middle of a global semiconductor shortage and many other supply chain disruptions. For products like Teensy, today the vast majority of available engineering time is going into managing supply chain problems.
APIs are not like software implementation, where bugs can be fixed later. Once an API is officially published and people write code which depends upon it, any change becomes quite difficult. Poorly considered APIs often result in a lot of bloat or poor quality workarounds to maintain backwards compatibility.
But new APIs are possible. Over the years, Teensy has added many APIs beyond Arduino's baseline. And in the future, more are likely. Near the top of my wish list is the generic function/member/lambda callback class for non-blocking I/O we've discuss a few times this year. But right now, with component shortages and work ongoing to revise PCBs for alternate parts, the sort of very careful consideration just isn't feasible
You are of course welcome to discuss ideas for APIs. I probably will save well considered proposals. Just please do so with the realistic expectation that little or no new API changes are likely to happen until you see Teensy continuously in stock at all major distributors.
But long term, yes, we do need more complete API coverage. The entire Arduino ecosystem has long needed this.