Well, on the other hand, if he did get it back, you can imagine it would be quite a power up, considering he is a swordsman.

He's been without it too long at this point. His regaining it would make little sense, but more importantly, it's become a defining feature of his, and should powerfully affect how he fights.

It's been far too long in the series to happen, so it definitely shouldn't. Besides, Shanks isn't a Devil's fruit user, so he wouldn't be able to reform his arm, like how Aokiji did in Film Z. At best, Shanks would have hoped for a mechanical rebuild, by some kind of doctor, like Vegapunk, for instance.
I doubt Shanks would get it back, anyway, though - his missing arm likely reminds him of the sacrifice he made for Luffy, so he would just leave it as it is.
Also, what Whiteflame says stands - Shanks is already strong as he is now, with only one arm. I think it's likely all he needs, anyway... except maybe against Teach.

If Oda intended it, I'm sure he won't be limited by DF powers. For one, Shanks eating a fruit won't be very cool. Secondly, even I can think of ways to get the arm restored without using an ability. There are all kinds of outrageous medicines and rare herbs and stuff in the world of One Piece. If it must be about DFs, it doesn't have to include Shanks eating one. It's easy enough to imagine a fruit user with a suitable healing ability. And, this might be a bit farfetched but, it might be possible for Shanks to use a "haki arm" of sorts. Ofc, that depends on whether Oda chooses to expand the uses of haki in that direction in the first place.

What's gone is gone. It reminds us and him of how he saved Luffy and tells us of his fondness for him.
I think the straw hat and his left arm not being there connects him and Luffy in their own little way.

Luffy would be extremely happy.