not too sure the disadvantages are really disadvantages. Having an audit at solely the entity level will be an advantage for partners that have otherwise risky tax positions on their personal returns IF they are in the highest tax bracket. If they are not in the highest bracket they will be either filing amended returns exposing risky tax positions or (I am assuming will be) providing the IRS sufficient information to report the tax in a push out calculation which will then expose any risky tax positions.
If, again, ALL the taxpayers are in the highest bracket then paying an entity tax would be efficient, assuming that the partnership has the cash to make the payment.
In some states a revocable living trust, used for avoiding probate, could be revoked in favor of a Transfer on Death agreement/account and thus allow the partner to be an eligible entity to avoid the new "regime".
The push in method has the risk that a partner will not or cannot (due to lack of available funds) make the payment on an amended return. Thus what partner would file an amended return unless all the other partners are on board??? And you may not find out that everyone is not on board within 45 days, thus missing the push out option.
The Push out election has the extra interest "feature' and also has the same issue that is the root of avoiding the new regime: who will take responsibility for being "that person". The proposal of amendments to the partnership agreement in determining the restrictions the partners place on the rep and the protections given to the rep seem to either raise contentions, even in just the planning stage (with greater contention during an audit) or, as I have seen mostly, a denial of facing the issue altogether leaving the choice of a rep a March 15th choice; maybe a September 15th choice!
BTW, the rep's decisions cannot be overturned by either state law or partnership agreement (301.6223-2(c )(1)) so pick a stable person who everyone trusts.