They will go probably the farthest away they can. That i can assure you. Clearly, in a project like this(utrust), having a lot of variety altcoins is a must. Because people want a wide number of choices or options that can benefit everyone. Because not everyone uses the same altcoins. So i think it is just right to assume that rhey will add as much as they can.
And for how long will they be using every altcoin added to the list? Honestly I do not know. But i think as long as it is still being used, they will not remove it.
I think they will choose for assets from the top 20 on coinmarketcap. Those are the assets with the most volume and mostly used.
It would be good if there will be a large range of different altcoins in there list of payments. The more altcoins the more this system will be used!
Cant wait