If they really wanted to, they could do a new rev of SWM that handled more than 8 tuners. Either by spacing the channels closer than 100 MHz apart, going a bit higher and/or lower on the MHz scale than the 975-1800 MHz range they currently utilize, or a combination of these.
Or do something more radical and put the tuners in the SWM module and have it deliver just the channel being tuned. They've already got 5 tuners on a chip as of a couple years ago when they introduced the HR34, so for the same cost they should be able to do 10 today, and if they wanted to do a bigger chip they could probably get to 12 or 16 without too much difficulty.
Then all they need to deliver down the coax (or cat5 - you probably wouldn't want to use coax unless it was already run to the location and cat5 wasn't) are the channels being delivered to all the attached receivers, as opposed to how SWM works now where an entire transponder's worth of channels are delivered for each SWM channel. At the very most, 16 channels totals only 250 Mbits/sec. That'll fit into the current DECA bandwidth, though they'd have an extra GHz of now vacant bandwidth available to play with if they wanted to give DECA more headroom and the ability to deliver 32 or more individual channels on a single coax. Outside of MDU environments, it is probably exceedingly rare for a single customer to have receivers/DVRs tuned to more than 32 unique channels at a time anyway.
This is all just wild speculation, they'll probably do something but I'm not saying it'll look anything like what I'm suggesting. I'll just say I'd be surprised if they plan on sticking with SWM as is forever. It was a big advance over the previous state of affairs, but the technology is something like 7 years old now. Getting the tuners out of the receiver would allow for the possibility of a TV that wouldn't need a receiver. Similar to RVU, only instead of talking to a Genie it'd talk to the SWM LNB/multiswitch. You'd only need one or (or two, for power users) Genie type boxes per account, everything else would either be a smart TV or a little box hopefully smaller than the current client that could stuck on the back of your TV, and ideally would be coax/cat5 powered so it wouldn't need a wall wart.