I started training in Iaido about 6-8months after starting Aikido. I found that there were no negative effect from training in both at the same time.
They are both different enough to not conflict with each other. I would imagine that it will be the same for Kendo.
When it comes to other open hand arts, for example Karate, JKD or Wing Chun for striking, Judo, Jujitsu or BJJ for grappling i would recommend that you practise in Aikido for a while first so that you have the base prinicial understood. This why you don't get confuse or cross over from one art to the other.
But at the end of the day the choice is yours, and u never know till you try