This is not a serious issue, but I think it will annoy me, so I'm curious what thoughts people have on it as well.
Regardless of whether abilities being turned into spells is a good idea or not, a minor annoyance/concern of mine that will certainly come up if handled the way its been done in the past is that you will no longer see your class abilities in the class section of the book instead you'll see:
"You gain the cantrip Pact Blade"
and no other information and so then you have to find that spell in the spell section to see if that is an ability you want. That's annoying.
This does happen now, there are class features now that read "You can cast etherealness once per day" and it bugs me, just enough, now when it happens, but it doesn't happen that often.
But when it's a key, class-defining, feature and you want to A) look up an ability B) compare abilities (e.g. the three pact styles for the warlock), C) quickly learn what a class does - not having the FULL information centralized in the Class write up is going to bug me, and I suspect others. Its a step backwards in quality of life. Its not game breaking, world ending, despair inducing, agony; its just the sort of thing that's going to be a "!@#$% it, that's in the spell section not the warlock section" moment at the table.
There is an easy fix for this, of course, put the "spell" abilities in the class write-up and this concern evaporates [though then you can split hairs over which spells this should apply to etc.], so this is not an argument against spellitization of abilities, its just a concern that I think may be worth mentioning to people so it can be part of the conversation with survey feedbacks and such.