if the "merger" goes through, then Sirius will be buying XM. they won't "combine" like channels, they'll simply get rid of one of them (most likely they'll get rid of every XM channel that has a Sirius equivilent.
for current Sirius subscribers the service will only get better because you'll continue to get the same channels you always had. plus you'll be able to get additional channels that weren't available to you before. if you don't want any of them you can just continue to enjoy the same old Sirius programming that you always had.
for current XM subscribers (like me), our service will change quite a bit. we'll have similar channel selections, but the XM channels we like will be replaced by the Sirius variants. on some channels this will be a good thing, on others it won't.
as far as pricing goes... "Subscribers who want their current subscription package will not have to pay any more after the merger. There will be new subscription packages priced below our current offerings." I see it as a win-win for both sides.