In researching a 401(a)(26) question, it was clear that separate asset pools did not comply with the intent of a26, even going so far as to note any outside indemnification agreements between owners.
Why does this matter? If the partners want to receive benefits based on plan asset levels, or they want separate asset funds to determine their distribution, then they want a DC plan. However, if they want the higher deduction levels of DB plans, the owners need to deal with the asset disparity issue.
When an owner wants their funds, what do you pay? The other owners don't want to pay someone else's underfunding off, but the DB plan needs to distribute benefits under the terms of the plan. Otherwise, they fail a26.

Of course, if the plan is underfunded, you would have the 110% current liability funding level to deal with, keeping the terminating HCE from receiving their distribution immediately.
I like the plan term allocation approach unless you have NHCE's. Then you have more serious issues, especially for underfunded PBGC covered plans.