Please, stop all these comments about the future of Geoffrey : his road is very well decided, already.
You need to know something more about the guy, before speaking about what you don't know :
1) Geoffrey had Always in his mind the Marathon, already when he was 18.
In 2011, we were in Eugene for Prefontaine together. I was there for the record of Moses Mosop on 30 km, and Geoffrey was with me, because his coach Patrick Sang (with whom I have great friendship) asked me to follow him in that period. Geoffrey ran 27'06" in 10000m, and one week later had the program to run 5000m in NY.
We went on track, 3 days after his first race, and I asked him to run 10 times 600m in 1'35" with 1'30" recovery. He was together some other Kenyan of the Group of Ricky Simms (Mark Kiptoo, Moses Masai and Mike Kigen), they went for 5 times trying to open the recovery till 2', and Always was Geoffrey stimulating them to start again. After 5 tests he remained alone, and started to run in 1'33" recovering about 1' only.
I gave him 5' rest, and after I asked him to run 5 times 300m in 42", with recovery of 3', only for doing some speedwork, since normally he didn't use to run fast. Geoffrey ran the first in 43", I started to speak together Lineth Masai without looking at the track (controlling the watch for calling Geoffrey at the start some second before his 3' of rest), and I saw Geoffrey passing on the track in front of mine when my watch indicated less than 1' after the finish of the previous test. So, I could see him running all the 300m in 43", but with a recovery of 100m jogging only in less than 30".
3 days later, he ran in NY in 13'12", and that one was the only time he went on track for something fast.
2) He Always showed big attitude for long distances, and wanted to run HM when still junior not for money, but because he supposed could be, at the moment, his best event (how the training he had with me in Eugene clearly showed : only athletes with great "mental endurance" can cut the recovery time in the way he used to do), and in any case the event he liked more.
He was also a perfect pacer for 30 km in the Marathon, at the pace of WR, the same year, enjoying the race, and this brought him to ask to run a Marathon in short time.
3) With Patrick and the managers (both Jos Hermens and Valentijn Trouw) we spoke several times about the fact that was too early to start the preparation for Marathon immediately, and could be better to stay some times in shorter competitions. However, the mind of the athlete was projected on running Marathon, and we had to wait his "normal" results for convincing Geoffrey to do a step behind, looking at cross and 10000m as main events at this time of his career. The advices of Eliud Kipchoge, in this process, were very important, since he is like the elder Brother of Geoffrey, wonderful person with great education and respect for other people.
4) Now, the plan is clear (we discussed about this with Geoffrey after his victory in Guiyang) : 10000m for WCh this year, World HM in the spring 2016 and 10000m for Rio, of course if he is able to qualify. His come back to Marathon is planned from 2017.
We don't know where Geoffrey can arrive in 10000m with proper and specific training (he never did before) : of course, under 26'30", but I don't know how much "under".
I think the record of 10000m is a weak record, compared with the record of 5000m. Kenenisa told me that, both the times he bettered the WR in 10000m, he was not in his best shape, and really he NEVER prepared 10000m in specific way. So, in spite of his medals (more in 10000m than in 5000m), Kenenisa was a specialist of 5000m running 10000m without specific preparation, and this explain the difference between the double of his time in 5000 (12'37") and his WR of 10000m (26'17") : 1'03", frankly too much for a REAL specialist of 10000m.
I think Geoffrey can stay inside 40". This means that, if he becomes able running 12'55" in 5000m, can run 26'30", and, if able running 12'50", can run 26'20".
The advantage of Geoffrey is that he's a front runner, and doesn't need rabbits in the last 3-4 km for running at his best.
Interesting challenge. I agree he can be the athlete giving new lymph to the event.