We just ran a tournament like this in San Diego! Our format was:
Limited Card Pool: Only Core, Deluxes, and Mumbad were in the card pool.
This could have been widened to include SanSan but we wanted to avoid getting Faust in because of the negative experience people were having.
Deck-building Restriction: Only one core box shared between both.
This would force some interesting choices. Do you go for the runner resources in Creation & Control at the expense of some of the more powerful cards you might find for your corp elsewhere? If you're doubling down on NBN are you going to lean into the Data & Destiny options and limit yourself to the core and mumbad runners? Or go crazy with one of the mini factions?
The reasoning here was that MWL hit a lot of core cards for non-core reasons. The card pool was limited as was, no need to further limit it. This, of course, meant half of our corps were NBN since Astro was not erratad yet. This is the only restriction (or lack there-of) that I'm conflicted about because it meant that it was harder to test these decks online. Obviously you're always going in knowing your power level is hampered, but a lot of people will auto-leave when they see you're not MWL compliant.
I'm looking forward to running another once the Flashpoint cycle ends. It's a great way to get some of the tier 2 cards into decks earlier than they might otherwise be. We saw things like Patron, Disposable HQ, Dedicated Neural Net, Voter Intimidation, Ibrahim Salem, and Brainstorm in those decks and those are far less common outside of that meta.