I thing so too, friend.

Thing of this as the logical extension of the analysis "you've got another thing coming". ;D

Can it be ambiguous to only use who instead of whom? If not, then it's probably not important, just feels painful for people who know the rules. That's as much an indictment of the rule itself as it is of people breaking it.

No, it can't[1]. However, vestigial marking of present-tense third-person-singular verbs is going strong and pretty much nobody considers the fact that it's completely useless as an argument against doing it.

The difference is that nearly everyone doesn't know the who/whom rule -- it is dead -- while nearly everyone does know the living pres.3sg rule, and they have trouble violating it even if in the abstract they might like to.

[1] The strongest argument in this direction is that no one in the modern day knows what whom means or under what circumstances it appears, meaning that when a whom is encountered it can only make them more confused.

I don't, you're certainly right and I even questioned myself as I wrote it.

Watch this and get back to us. https://www.youtube.com/watch?v=J7E-aoXLZGY

"I thing" <-- while knocking OP's grammar? Yes, I'm silly too :)