Generally speaking, each transponder can hold 12 channels and each market has about six stations of interest. The smaller markets we are now dealing with probably fit that bill more than others that have passed.
Given the above, a 32 transponder satellite such as 121 can host up to 64 local markets. However there seems to be a lot of space reserved for Internationals on 121, and a few that are being sold from that location.
There are currently 52 non-LIL channels on 121, enough to fill 4 1/2 transponders. If E* reinstates their plan to have 100 Internationals from 121 it would consume 9 full transponders.
Leaving only 22 for locals, or 44 markets.
There are seven markets currently being sold from 121. Which means filling 121 would allow for 37 new markets there. This does NOT leave room for mirroring HD may or may not be placed on 105 so that it may be seen in 121 markets without having two Superdishes.
105 is scheduled for replacement (later this year IIRC) and currently has 24 transponders of a slightly larger capacity than the 32 transponders on 121 and the other E* locations. However, the lower power of 105 is causing them to lose capacity by providing more error correction. We still can estimate the transponders at 12 channels each, but we only have 24 to begin with.
The HD currently on 105 is not being sold from that location. Most of it has been moved to 110 and shouldn't be counted against 105's capacity. CBS-HD east and west are currently on the wings.
The plan was to have 50 HD signals on 105, which would consume all of it's current capacity. With eight channels on 110, that knocks the requirement down to 42 - or 21 transponders - leaving room for only 6 local markets IF space is left for HD. Since there are already 15 markets on 105 it appears that 50 HDs is no longer a goal.
So let's guess that the two CBSs will stay and the other transponders will be all locals. 23 transponders allows for 46 markets, with 15 already being sold. 31 new markets could fit there.
37 on 121 plus 31 on 105 = room for 68 new markets beyond the 101 currently uplinked and being sold. A grand total of 169 markets.
If the new 105 satellite provides enough power to run 32 12 channel transponders then an additional 16 markets could be added then. Or 185 markets.
We need 210. 25 markets would require up to 12 more transponders.
Depending on just how small those markets are (many will not have 6 channels) they all could fit on 105-121.
Personally I'd ditch the internationals off of 121, allowing for 9 more transponders - (OK 8 more leaving the internationals that are already being sold there. ) With a couple squeezed on Dish500, they may just be able to shoehorn it in.
If they ever built another uplink center, say on the east coast somewhere, they could squeeze even more on to the spotbeams on 110 and 119. That would give them even more flexibility and potentially eliminate the need for putting anyone on the superdish. It must be cheaper to build superdishes and launch new FSS satellites.
Its more than cost issues, even if it were have been cheaper to provide all the consumers with a SuperDish it could cause them to not gain as many subscribers due to dish size. Wait until DirecTv adds those additional markets with their oval 3 slot dish that is a good bit smaller than the SuperDish and see which one people prefer. Their dish is cheaper than the SuperDish as well.