Funny how people rationalize things.
Now that AMDs multi GPU solution is catching up to/surpassing nVidia, it isn't a desired feature? DX12 promisses better multi GPU support, Oh Well it's too hard to code for all applications. Lower tier cards benefit the most from multi GPU, let's make it a feature on the 'high end' only.
The cards should have FULL access to the bandwith available, even if they can't fully saturate the bus yet. Linking cards with a ribbon? What is this 1998 or something?
LoLoLoL
In fact if you ask anyone for advice on graphics cards, those with common sense will always tell you to prefer single card of lower tiers over a dual GPU solution, unless you're buying into (one of) the most powerful cards already and need the extra performance. That 'rationale' has been as old as SLI or Crossfire itself.
The cost/perf advantage of dual GPU solutions is 10-15% over a more powerful single GPU, on average. That's 15-20 bucks for midrange cards, 30-50 bucks for upper mid range/high end, taking into account already that games don't scale perfectly. With that minimal win on purchase cost, you do get a lot of drawbacks, of which lacking SLI/Crossfire support in specific game titles is the biggest one and the only one that also applies to the high end cards. However when you go into lower price ranges, the VRAM/ bus width issue pops up. Also with AMD cards, but Nvidia's suffer more readily from it. You talked about 'having full bandwidth available' which I don't really understand. PCIE lane bandwidth, VRAM bandwidth? Both ARE available... you're just bottlenecking on VRAM very fast.
As I've pointed out, I have practical experience with midrange cards on SLI. It was not a good graphics solution, the end result was less consistent performance with a pretty significant price tag. Back then it was early Kepler days, when AMD was making the news with their frame pacing issues. Back then, I drew this conclusion, not today.
Today however it's even easier to draw this conclusion, with DX12 placing the workload for solid SLI support not just in the hands of Nvidia+AMD but also explicitly in the developers' court and especially if you look at current day DX12 status where multi GPU support is hard to find. DX12 promises a lot of things, because Microsoft is selling it. We have yet to see the real advantages of it in games.
And it's in the forum anyway, not the front page and shows the level of interest in Ryzen. The front page doesn't cover it quite enough in my opinion.