I know the answer is not 100%, but hear me out.
I've been dealing with a strained iliopsoas for 10 months or so now and have been mostly lifting weights and cycling. Did some swimming for a while also, but that stopped a while ago. I've been trying to get out and hike and walk and occasionally, I'll try to throw in a little jog into my routine. For myself and my daily fitness routine, that is sufficient.
Throughout my running and coaching career, I've seen anecdotal evidence of people coming off of extended cross training stints with very little running and then performing quite well. I remember being at an early season invite back when I was in college and learning that the women's winner had spent the previous 6 weeks of training in the pool and had only come back to running for a week before the meet. I believe that Blaise Ferro spent the vast majority of his senior cross country season doing alternate workouts, and he ran really well at Nationals. I'm sure there are other examples.
Today, I was in a different town and there were some hills on my walk route. I discovered I could run up them almost completely pain free and that got me thinking, how good could someone get for running by doing mostly cross training and then doing only specific running workouts?
For instance, it should be pretty obvious that you can get more volume of sub threshold training done on a bike than on foot. Could you reap the cardiovascular benefits of cycling and then create running fitness by doing, say 10 x 200 @ mile pace once a week?