It shouldn't complicate things at all
Tested on toro, working as expected. Meaning, everything works except mobile data for me. Behavior is exactly the same as Unlegacy 7, so no surprises there. I'm on Page Plus (a Verizon MVNO) and that complicates things sometimes. Still, I was hoping that maybe it would just magically work on Slim7. Oh well... Thanks anyway, it is a very sweet ROM!
With PP now being a VZW MVNO, it shouldn't complicate anything (as long as your are running toro hardware). I took my toro to Tracfone (a split MVNO - between T-Mobile and VZW), and went specifically to the VZW side of things (two reasons - T-Mobile has always had signal issues here - or anywhere else, and VZW has Just Plain Worked - I'm a former VZW prepaid customer). Page Plus used to be a pager AND cellular service provider - with their own towers. I'm running Slim 7 beta because I wanted an SELinux enforcing ROM that ran N on my hardware; so far, Slim 7 is the only such. Even Lineage OS 14.1 (also unofficial) dropped back and punted to permissive - not enforcing. I won't touch MM with a ten-foot pair of chopsticks because performance bites compared to N on toro.
Followup - Slim 7 is now updating apps - all 77 of them from a previous ROM. Even better, for the first time on N, SafetyNet works (nothing broke it). I ran into a solvable problem with Android Pay, though - my VISA debit card doesn't support it (Android Pay, that is); rather amusingly, it DOES support VISA Checkout. Fortunately, that means that all I need to find is a debit card that DOES support Android Pay - time to warm up my Google-fu. (As expected, the Google-fu paid off; two banks near me have multiple branches where I can apply (and even pick up) a prepaid card on the spot - PNC and Wells Fargo (AKA Stagecoach Bank), and their prepaid cards are SPECIFICALLY supported by Android Pay. Rather oddly, a whole lot of prepaid cards are specifically denied - and from BIG banks, at that - CITI and AMEX tell their prepaid clients to hold the phone/phablet/tablet and don't even bother to try their prepaid cards. In addition to PNC and Wells, Bank of America says "si" to prepaid and Android Pay - the minus (for BOfA) is that they aren't the closest bank branch - rather amusingly, the closest bank branch where I can get a prepaid card used to be, in fact, a BOfA branch - it was acquired by PNC when BOfA did "the great branch thindown" in several states - and I don't live in either North Carolina (the current HQ of BOfA) or San Francisco (the historical beginning of BOfA and, interestingly, what is now VISA USA (originally BankAmeriCard).