I had a look at the format from last season. In that version the 14 teams were split into two tiers based on league position, and you played two teams home-and-away. You couldn't play a team from your own league or from your own tier (vaguely similar to the Champions Cup format) but you could play two teams from the same league.
They could do a similar format with 20 teams, possibly split into two tens, with 5 in each tier.
In that case Connacht would be in the top tier and would avoid the top 3 qualifiers from the other leagues.

So the options would be:
Brive, Perpignan or a promoted French team, and
Worcester, Bath or an invitational team

But potentially it could be two French or two English.
Might actually be more likely to be a Romanian than a Georgian team if they add one more as they have stayed out of the RE Super Cup so far. Baie Mare are the Champions but their season runs through the summer now and Timisoara seem to be making the early running.

I would take Bath and Mont-de-Marsan for a bit of variety, or a random Tier two team for a proper adventure ...

neill_m wrote: Glasgow can still get the Heineken Cup spot if they win the playoffs which would see Munster drop into the Challenge Cup. However this is a long shot in reality.

You're right. I never spotted that rule. When they originally launched the URC, the rules were that you could in theory win the URC and bizarrely not qualify for the Champions Cup, but they must have slipped a rule change past me ( www.unitedrugby.com/about/competition-rules ). It's odd that Edinburgh would still progress as Scottish/Italian shield winners despite there already being a Scottish representative but them's the rules I guess.
As you say, it's a long shot. You can get 80-1 on Glasgow winning it.

Glasgow can still get the Heineken Cup spot if they win the playoffs which would see Munster drop into the Challenge Cup. However this is a long shot in reality.

No confirmation on the Challenge Cup format for next season but the line-up so far looks like:

Glasgow
Scarlets
Connacht
Lions
Benetton
Cardiff
Dragons
Zebre

Wasps (unless they beat Leicester away on the last day, in which case London Irish)
Bristol
Newcastle
Bath
Worcester

One of Toulon/[strike]Lyon[/strike]/Clermont ([strike]Toulon are favourites to win the Challenge Cup and progress, Clermont would then have to make up a single point on Lyon on the last day, when they're both at home to title-chasers[/strike] - should be worth a watch)
Pau
Stade Francais
Brive
Two from Perpignan/Mont de Marsan/[strike]Nevers[/strike]/Bayonne/[strike]Oyonnax[/strike] (bookies have Bayonne as firm favourites to win Pro D2 leaving a likely play-off between Mont de Marsan and Perpignan)

Plus however many other teams they add. With 19 teams, maybe adding Rugby Europe Super Cup winners Black Lion from Tbilisi would be the obvious move. Unless they want to add five teams and use the same format as the Champions Cup.

The format this season was three pools of five, playing each other once. If they go to four pools of five, there would be the possibility that we wouldn't travel to France for the first time since forever (as two pools would only have one French team and we might get them at home).
They will almost certainly change the format though as that one left a week off for everyone due to the odd number, which was made up during the first leg of the round of sixteen, but with one less weekend in the calendar next year, that won't work.
My guess would be two pools of ten, with a format vaguely similar to the Champions Cup, but even more confusing :evil:
Whatever the format, with only four games in the pool, and more URC teams than everyone else, [strike]not every URC team can travel to both England and France (if my maths is right)[/strike]. So we might have to make do with Lisbon or Tbilisi (or Newport).

EDIT: Now I think of it, they will probably want to keep teams from the same league apart, which would mean all the URC teams could go to both England and France. Some English or French teams would play two games in URC land in that case.