I've heard this from other people too, but as an owner of both LLC's and Corps in the past, why is it so difficult? Just sell one company's assets to a new company.
If everyone is on board for the 'new' structure, then this should be trivial. If you have investors, you grant them new shares equivalent to their old LLC member %.
LLC"s have huge advantages too, if you dont plan to raise money, or only do it from a few people. The fact that you can allocate losses and gains regardless of ownership % means that you can allocate tax losses to an investor who may only own 20%. Them taking a tax loss is effective to them not paying more taxes, so it is a form of benefit for them.