The way to incorporate resistance training would be to come up with a simple periodisation scheme. For instance, you would drop running volume a bit for 6-8 weeks and focus on 2 heavyish full-body resistance sessions per week, then cycle back to a running intensive schedule for a couple months, dropping down to one or two moderate maintenance resistance sessions per week, etc... Periodisation has the advantage of giving fitness elements/body parts some extra rest. It allows you to put your main effort into a selected activity/element while maintaining the majority of what you have acheived in other areas.
I used to do a fair amount of distance running and I found it gave me more than enough stamina for Aikido. Since then I got hooked on interval training and find continous aerobic training of any type interminably boring.
At first I kept up 2 or 3 20 minute runs per month, then I couldn't even take that. Now my HIIT sessions are usually 15 minutes or less, and my 'continuous' sessions are 10 minutes of moderate jumprope/run intervals in the park sandwiched between two 5 minute warmup/cooldown runs. Between the two workout types, I rarely get in more than 2 total sessions per week.
Yet, on the whole, I've found intervals even better for Aikido, and the exercise volume is very low, which means almost no injuries for me, where I was plagued with them when I was a runner. Plus there are other benefits which I won't go into. The bottom line is that I think high intensity interval training is the closest thing available to a miracle general health tonic and fountain of youth.