You know what I want to see them do? I want to see them bring back the 50/1.0L. Remind the world why the EF mount was made to be what it is. I want to see them push the envelope and see what could be done with today's manufacturing techniques and materials. You know your stuff is outdated when even a company like Sigma can beat your 35/1.4L for bokeh quality, corner sharpness, and secondary spectrum control. Then design an affordable series of lenses with emphasis on durability, like a 50/1.4 II, or a simple 50/1.8 that isn't plastic.
Canon used to be the undisputed leader of designing novel AF lenses. This is the company that gave us the TS-E 17/4L, 50/1.0L, 85/1.2L, MP-E 65/2.8, 135/2L, 200/1.8L, and 400/4L DO IS, among other amazing technologies. But all we see these days are uninspiring, conservative, incremental designs. Nothing that pushes the envelope, nothing that makes us feel like we just *have* to try this lens because it will let us get the shot that no other lens can.
While I agree with most of your sentiments, but many of those "golden years" lenses has some serious issues. The 50mm f1.0 L is horrendously soft wide open, The 200mm f1.8 was closer to f2 in reality...and was heavily front heavy...it easily nose dived on a pod becuase the tripod ring was put in completely the wrong place. The 400 DO is widely regarded as softer than the 400mm f2.8 or 400mm f5.6..or even a 300mm f2.8 with a 1.4 TC (which really questions the need for that particuar lens).
While Sigma have a fine 35mm f1.4, my Canon 35mm f1.4 has performed faultlessly over the last 6 years...I have the Canon version and the Sigma version wasn't available and it produces fantasticly sellable pictures. To me, a lens is a lot more than chart results and sharp corners.
A new 100-400 L would be a game changer. The mkI version is one of the most versatile long lenses available and it's very old and certainly needs a re-work. An IS system which didn't come of the ark (it was one of the very first IS systems ever put into a lens)...an AF system which faster than pedestrian....and a sharpness to equal or better the 400mm f5.6 would be very nice. I'd buy one in an instant....I could lose several lenses in my bag to combine into this one lens.
At a guess, I'd say these are coming:
a new ultra wide, say a 14-24L (although a 12-24 would be sweeter)
A TS-e 45L and TS-e (longer than) 90L with improved macro capability
A 180mm L Macro replacement
A 300mm f4 L IS replacement
That's six, I'm sure there's more!
I'd like to see a 24-105L update and a 16-35IIL replacement.