But as the block rewards diminish from halving it will approach 0, so that will leave the only incentive for "miners" to secure the network to be transaction fees. At that point transaction fees will have to be extemely high to justify all that hash power right? So I can imagine it could get to the point where transaction fees exceed the value held in some wallets and you get stranded assets.

Alternatively, if transaction fees stay low, there might be very little incentive to secure the network with hash power and you could end up with fewer and fewer miners controlling the network and a 51% attack becomes quite feasible.

I'm really curious how this will play out over the next 100 years.