....If you answer to my question on what question I did not answer is none.....Actually you are telling me I answered all your questions.
My reply previous to this one was crude, my apologies, but I'm not going to play this game so try to be serious and stick to bonsai, please.
The result would be a trunk fusion bonsai.
Not in the every day sense it isn't. This project is unique (if I can be so bold and use that expression and open myself to yet another unwanted lesson on English grammer/definitions) because the centre trunk (the whole tree for that matter) isn't exposed.
No it is not advanced.
I disagree if for no other reason than the fact that it hasn't been discussed anywhere that I've ever seen.
If the species used is possible to graft to each otheres, there are no other complications involved than in grafting.
That's not he issue. Your first reply was
"it will work".
What will work? Will it (they) survive and grow? Of course they will! It's the results of it growing and surviving that is the question and the basis for the project itself..
2 POSSIBILITIES, just for starters:
1). Is it possible for the centre trunk (grapefruit in this case) to fatten in such a "dominant" fashion that it can create "lenticels"? (I'm using quotation points so please, not another lesson, OK?)
2). Can or will branches of the grapefruit push through the bark of the orange leaving you with an orange trunk with emerging grapefruit foliage, blossoms, and fruit?
There are several other questions but these are the initial ones.
Ps. English is not my mother tongue and I am sure that if you were compelled to speak my language you would appreciate an ounce of tolerance. Can we agree on that? Thank you.