Late comment...
Was thinking about this...
The issue with removing some wort, you risk contamination, but then so do you with suckback - even if your blowoff tube is immersed in sanitizer, you risk pouring some sanitizer in your beer.
Also, what do you do with the wort? You could prime with gyle if you are bottling or cask conditioning or you could simply add it back, like a staged fermentation, or a combination.
I have not fermented in my 5 gallon carboys lately. I used to more often, but the problem is, different recipes and different yeast have different degrees of blowback and while sometimes I get away with, not always... I'm also doing all grain now, and haven't completely dialed in my equipment and evaporation loss, so my batches are anywhere from 4.5 to 5.5 gallons (though the last two seem to be settling about 5.25). That would just barely fit in my carboys, so been using buckets. I do prefer carboy fermentation, because you can easily see what's going on, but I think I'll invest in a couple of 6.5 gallon carboys. I really hate plastic since it breaks (and breaks down) on me and is harder to clean. I also do sours and won't let those touch plastic. My last sour blew out on me pretty good. The neck was nearly stopped up with trub, but I also didn't use a blowoff tube (didn't want to get sour in my blowoff tube - kind of hard to clean). I ended up tossing a sanitized towel over it to minimize the cleanup...
I think if I end up with too little (4.5 gal or under) I would use a 5g carboy, but otherwise, it has the potential to blow out a bunch of your beer (my greatest concern). Depending on the recipe, it can be quite a mess as well as risk ruining your beer.
