A few points:
Might&Fealty will not be subscription based - instead you buy 'gametime'. Once that runs out, you are finished, no need to unsuscribe or any similar hassle.
Next, Tom did mention that cost per month might still be tweaked. I expect that those 20€ will buy you more than 3 months...my personal benchmark is that for a lightweight game I would gladly invest 5€ per month, would be willing to invest 7€ per month (the current price of M&F) and would be willing but hesitant to invest 10€ per month. In addition Tom mentioned that its possible that he will add a free trial period (which I think would be absolutely necessary).
To me there is no different between subscription and whatever you just described. Point is, you have to pay per month.
The fact that everything is still up in the air, is really a problem for me. In most crowd funding schemes, you know that if you pay a certain amount you will get the game(if the game ever gets finished). With this, and any MMO really, it's a huge problem that you don't know how much more you will have to pay when the game comes out.
About the trial period, Tom has in the past been firmly against this, because you need all players to be committed to the game.
On the other hand one of his actual ideas was a lite subscription, where you could play a limited number of characters for no monthly fee, but you still have to buy the game though.