There is no cap to UTXO set size. Currently your node stores all this in RAM. As things like stamps and general mass adoption increase UTXO set size, it will become harder and harder to complete initial block download for new nodes, particularly in the global south.

UTreeXO is a brilliant proposal to solve this issue and bridge nodes will serve as an initial stop gap to avoid a soft fork. But eventually trust in the resilience of bridge nodes will erode and convince people to soft fork in such a way that bridge nodes are no longer required, ie proofs stored in blocks. Tradeoff here is longer block validation time burdening low bandwidth internet nodes.

No perfect solution means we will have blocksize wars 2.0 to determine the future.