I get that. I still can't see Finn taking on the Undertaker. If he were to be the opponent, I think he would have to have been brought up and established himself a bit already.
Facing Taker can be how you can establish him.
You enter the night with most people not really knowing who he is, you leave the night with a bunch of people thinking whoa this guy just showed up and went toe to toe with Taker. You're a made man already.
There's not really any perfect solution because with the options for Taker because there's not much in the way of a huge fight available. I've said in here I'd love to see him vs Jericho, but there's not really anything available on the grandiose level that you expect a Taker match to have. In fact Jericho, while obviously jobbing for a long time now, is really the biggest name value candidate.
Like I said, Finn is a blank slate, you can put him at whatever level you want to. You aren't going to get the Roman revolt because A the smarks love Finn, B Finn isn't some green guy with a bunch of shortcomings. Finn is already Finn, he's been this good for a long time before he got to WWE, he doesn't need to be developed any more.
If you bring in someone and treat them like they are something special, and they actually back it up, then people will buy it.