KISS - Just divide the total amount of assets between the different platforms and list them with the same name and issuer.
Is that not workable?
It's workable but could be better (less work
I gotta start from simple to be able to begin to comprehehend more complicated. So e.g. if my asset is a potato that I have grown, I'm putting that potato on sell on FIMK, NXT and XCP AE's. The asset is sold on FIMK AE and before I have time to manually cancel it on the other two AE, it is sold also on both of them (e.g while I sleep). I have sold 3 potato assets and I have only 1 potato, two buyers not happy at all, express their opinion publicly, etc... If there was way automatically transmit info from one AE to others, so that when the potato is sold, the sell orders in other AE gets cancelled, that would be better. Number of assets/potatoes is not essential, same if I have 3 potatoes and all of them get sold at one AE at same time. The solution of having 3 potatoes and putting one on sale on each of the AE is workable but not ideal.
The tech problem of linking info from one block chain to another is not simple - sync of differently timed block chains remains unresolved math problem. Ripple protocol is ancient and tested decentralized third party trust system, and could function as desired also in this context.