I'm thinking of purchasing NUC11PAHi7 . I know that it supports DDR4-3200 but I already have 2X16GB DDR4-2666 that I was using in my NUC 10 and was wondering if this would work okay for the time being?
There should be no problem to use DDR4 2666MHz RAM, you should try. On the Compatible Product list there is 3rd Party Validated 2666MHz Crucial memory. As you understand, the NUC performance with 2666MHz RAM will be degraded comparing to performance with 3200MHz RAM.
