In order to fit as many figs as I can in the limited space that I have for over-wintering I was thinking of transplanting 2 trees in one 30 gal container. I have 38 in 5gal. buckets and only room enough for 8- 30 gal pots in my shed. I guess it would be like having a very large plant in a 30 gal pot. Has anyone tried this?
I assume that I'll have to root prune more often. Are there any other considerations?

You may want to ask someone that braids fig trees because their roots literally intertwine. These fig growers should be able to describe growth and fruiting habits.

I started out in figs by putting 3 varieties each in two 12 gal pots. Total six varieties in two 12 gal pots. It worked great. Found out I liked Paradiso and Strawberry Verte. Vista was productive but lesser eating quality. Black Jack, Blue Celeste, and another I can't recall now were rejects.

Based on my experience you could put 6 varieties in a 30 gal pot and hope for 20-40 figs per variety. I'm fruiting 20 varieties now in 5 gal pots to decide what to keep. 5 x 6 = 30 gal. Seems to equate in my world.

I've fruited 3 nectarines in a 12 gal container and could cite many other similar examples. Those who say you can't probably haven't tried.

Picture is 4 nectarine fruiting in a 30 gal pot. This is year after planting. A lot more fruit the 3rd yr.

One downside is if one tree grows faster it might shade the other.  I would think risk of losing one is higher than one per pot.

Some people Pleach fruits or flowers which involves twisting or braiding the plants together.  It is possible and you can do it, but as Phil says if you mis pair them and have a tree growing faster than the other, it would be out of balance, if you do it, I would pair varieties with similar vigour in the same pot.  Another option would be to have one you believe to be a good rootstock and graft desired varieties onto it, then you could keep for a few years the varities you grafted in smaller pots with root pruning until you know that they are compatible with the rootstock, may help even out any vigour issues as well since they should gain some vigour from the rootstock but you would still need to make sure not to put a slow grower on with a fast grower in my opinion.

No pain no gain. If it were trees that I could replace and I could only have them by planting multiples I would certainly try it. Most shrubs are grown with multiple cuttings. You might have to keep one variety pruned to keep it from over growing the other. I will start a trial tomorrow, I want to know. I don't recommend multiple citrus grafts on one root stock because one variety usually grows faster than the other.

Balancing the vigor takes about 2 minutes per pot a couple times a year. I spend amazingly little time pruning anything in pots. It's simply not an issue. And there's no more risk of losing a plant. I'd rather have 6 figs each in a 5 gal pot than 6 in a 30 gal just because the smaller pots are easier to move. But it can be done either way. And my previous estimate of 20-40 fruit per plant is conservative but it does depend on length of growing season. I can get more than that in my greenhouse with a long season.

Maybe you could put something in the pot dividing the two sides to keep the roots seperated. I don't know how well thatll work though

I think you will probably do ok with 2 in a 30 gallon pot.  I would put 2 varieties of similar size and growth rate.

Two in a 30 gal,
with proper training/pruning 
is no problem.

Just have to feed them more often than inground trees.