I thought this would be met as imminently logical, but...
It seems to me that the #1 invitational bump after a Michaels bid for the majors and simple preference to hearts (e.g., 1♣-2♣-P-2♥-P-?) should be 2♠. Here's why:
1. If partner has a 2-2 yarb, he can pass.
2. Advancer can bid 2NT, 3♣, or 3♦ as a "try back" bid.
The main objection was "but that shows 6♠/5♥." Why? I mean, sure, it sounds like longer spades, if not discussed. But, then if you must have that meaning (rather than just having someone bid 4♦ eventually as choice), then perhaps make 3♥, the expensive bid, show that.
This also allows Advancer, with that 2-2 yarb, to always bid 2♥, smelling the likely bump, but saving the two-level. Eight tricks might be the limit, or worse. I recently played 4♥ (which was an overbid) with that 2-2 yarb, -500 (I should have settled for -400 rather than taking the insane line), where 2♠ would be -200 and a fair result. Actually, 2♠ makes, apparently.
I have no idea why this was resisted. It seems obviously superior.