RR, you ask such good questions. It is such a good question that there is nobody here who can really answer with any specificity. Any decision that would exclusively rest with the Pope and the Magisterium. Personally, I don’t think it is my place to suggest what compromises are possible. The big picture is my focus- Unification as Christ wants. Everything is the perogative of Bishops and above. I hesitate to even speculate as it somehow infers that my opinion is important.
But, it is fun to speculate.
I think one poster said it the closest: Nothing on Doctrine. The Truth is the Truth.
But there is great wisdom with regard to liturgy and discipline. The reason we have so many different Rites is that it accommodates cultural differences. While often asserted on here that any accommodation is a threat to unity, anybody who has attended Mass outside their own culture or another Rite will understand that the Church is more tolerant of liturgical differences than we imagine. This being said, with a little study one quickly realizes that while the appearance may be different, the essentials are in place regardless of culture or Rite.
And for some, a re-unification would be much easier (ie. Anglican and Lutheran and even possibly some more liturgical branches of the Wesley-tradition) as they have retained much of the liturgical practices. Similarily, a Catholic Charismatic Mass would appeal to some of our separated charismatic breathren.
The more challenging denominations are those whose congregations revolve more around the charisma of the minister. They have a leader who has never really had to submit to an earthly authority. He gets to write his script and do as he pleases.
Regarding disciplines like a married priesthood, of course this would be a discussion item. We allow married priests in other Rites and we allow it in the Latin Rite if it the conversion of an Anglican priest.
Imagine that a major denomination reunited, what are the practical challenges beyond what RR raised. Availability of Priests and Catechesis.
I think that there would be some type of transition period granted whereby we would have to educate all the new incoming Catholics on the faith in preparation of Confirmation. The laity like most on CAF would have to really step up to the plate (are we willing to do so? We talk a good game here!).
Then, when we had all these new confirmed breathren, how could we accommodate them regarding Mass without also requiring to dissolve the faith community (defeats the principle of macro reunification vs. one-by-one) and causes chaos.]
I think there may be a need for a lessening of the obligation for Mass for a generation for these new Catholics (not the rest of us). We could ordain rather quickly their Pastors as Permanent Deacons and institute some type of allowance for Communion Services on Sunday with a periodic visit of a Priest for say a monthly Mass. After the Communion Service, there may be some allowance for components of their traditional service. In fact, since they are used to hour long sermons, it could be how catechesis occurs. This is similar to how we don’t have eulogies delivered during the funeral but after it is concluded.
The challenge is huge but imagine how pleased Christ would be if we were one as He desires? Just the thought excites me!
Sidebar: I watched Journey Home Roundtable last week. Two of the panelists were former Lutheran minister who are now Catholic Priests. Anyway, one of them mentioned that his wife was Catholic when he was a Lutheran minister. It was never clarified if they were still married, had gotten a divorce, or she had died.