No reason in rulebook terms why they can't wind up in the LL. There is no fixed geographical boundary and adding them would round things off at 20 clubs. The angle I find interesting was the snippet in the Evening News that some LL clubs were concerned that WoS and EoS clubs were going to be invited to make up the numbers in the "conference" instead of them. Sounds like that was a threat made to them by the SFA.
The OF and Hearts maybe want to dictate who gets to be in tier 5 so they have the strongest possible opposition for their B teams by having clubs like Darvel, Auchinleck Talbot, and Clydebank around rather than Edinburgh Uni, Gretna, etc. Still don't see how they could legally get around the Club 42 playoff agreement though, so it was probably just a case of Maxwell and Petrie knowing which buttons to push by threatening a solution imposed from above to address the LL pro/rel logjam.