I don't know of any issues. You’re mainly just giving up the ability to perform rich queries. The db search is a few LIKE statements.
I don't think we've tested millions running db search - but the only issue I can think of for normal usage would be the User page in the UI since we’ll be paginating over lots of users.
This should work ok - but pagination tends to slow way down as you get into higher pages,.
One can always flip on Elastic and run an index, so not much harm in trying it.