New Comparability v. Cash Balance Plans

[IRC401]

If the IRS eliminates "new comparability" plans, wouldn't it be possible to recreate the same plan as a cash balance plan with accruals based on the same investments as in the DC plan (as opposed to being linked to US Treasuries)? [OK, so you would have to deal with QJ&SA waivers and PBGC premiums and waste money on actuarial fees, but couldn't you get to essentially the same position?]

How are actuaires doing 401(a)(4) testing for "self-directed" cash balance plans? As far as I can tell, the big firms regard that info as a trade secret, and the IRS pretty much lets them do what they want.

It seems to me that unless the IRS issues some guidance on how to do (a)(4) testing for cash-balance plans, it makes no sense to go after new comparability plans. Am I missing something?