Should I say yes or no, when product owner asks for a certain feature, but it could increase the complexity of the system? More info on description

Hi, my team’s product owner has some requirements which will increase the product’s complexity.

For example “Hey we want customers to start using the new ui(think of it like Reddit’s new ui vs old ui)

Let’s call this new ui as (v2), and we cannot force v2 on end users.

We have to give them a “try it out” option, which allows them to experience the v2 feature, while still being in v1.

An Account has many portals. And a portal has many users. And these users can belong to multiple portals within the account.

The PO wants to give this option to each user, until one user decides, that they want to move to v2, then they can publish the v2 feature to everyone in that portal.

Achieving this requirement would mean, that we have to maintain a lot of states to know which user is in which state.

So here is my query, how do I see this problem. Should I strive to make customer’s life easier, with the side effect of making the system complex.

Or I have to request the Po to make some decisions that will force the v2 ui after some fixed time?