Adjusting the colors to the destination gamut seems more acceptable than just de-activating filters since most of the popular CMYK profiles fall pretty much inside the sRGB gamut. The out-of-sRGB-gamut colors can be adjusted using the relative colorimetric intent (probably it would be a good idea to nag the user with a warning when this happens) but in my oppinion as user that's completely acceptable.

I agree that allowing untagged CMYK would be a bad idea. Thanks to poor design decisions in popular software packages, users tend to think that the important thing is to have CMYK and color profiles remain like something rather obscure that it shouldn't be touched (i know because I was one of those clueless designers ranting for CMYK knowing nothing about color management :-p) Thanks to being unable to work with early binding with Inkscape and GIMP I got used to late binding and once I saw the benefits I realized that it's better. I finally understood that when designers (like me) ask for CMYK they're actually asking for a way to use black as a spot pass. Pantone colors can be used with both early and late binding. Most of the designers I know use the formula books -which have Lab color values- in an early binding workflow, thinking that they will get the "right" CMYK values and they don't realize that the colors are being mapped to the generic CMYK profile they're using. So, truth to be said, maybe it's better to adopt a late binding worflow with the ability to "force" CMYK values (for blacks/grays or for specific CMYK combinations) rather than worrying too much about how to deal with CMYK and filters and all.

From my user p.o.v. everything seems pretty much ready for a print

workflow. We just need to make it more obvious in the UI, and it looks like something that can be achieved improving the fill+stroke dialog and the auto-palette a little.

Just my 2 cents.