I dunno. If MMA puts any pressure on traditional martial arts, it is on practitioners, not on systems.
Most of the usual "MMA vs Aikido" stuff seems to fit here. In what venue are MMA people who have trained for 6 months "eating Aikido people alive?" The ring? Give the Aikido people 6 months of training and see what happens, right? Are the MMA people stepping onto the mat to learn Aikido, either traditional kihon or internal strength principles?
I was thinking more along the lines of systems evaluating teaching methodology, developing combat styles, kata and the like. I believe a good example of this was the Gracie style jujutsu introducing effective use of the gi in the ring... I think the personal struggle practitioners experience is real, but in the sense personal skill will always exist as a comparative metric.
The venue to which I was referring was not necessarily even ring fighting, but simple situations like "don't let your partner throw you" or "don't let you partner grab you" or "don't let your partner hit you." I think MMA in particular is more advanced in the "independent movement" theory, mostly because they want to [independently] kick your butt. Aikido stills talks about 4-legged animals and connecting to our partners. MMA is a great resource to illustrate, for example, why we do not want to connect to our partner.
Are MMA people stepping onto the mat to learn aikido? Not to any measureable amount of which I am aware. However, aikido has done a poor job of marketing our skills to the professional fighting circuit. My personal attitude is that if I know a judo player, or a MMA fighter and they are looking for an edge I will help them to the best of my ability. 2 of our judo guys just medaled at US Nationals - I could not be happier and if they ever asked I would be pleased to see how aiki could help them play better judo.