That's a beauty, it would be worth it to lap it flat to me. A shame that you can't use it as is. That dish would make a convexed edge not concave. A convexed edge on a knife is MUCH stronger and stays sharper longer. Would be interested to see how I would do on a razor.
Ok, I had a good look last night and it's not just dished lengthways but also crossways. I'm gonna try and lap it so that it remains more or less flat crossways but stays dished lengthways. Gonna be fun! One thing I will say is that it's a lovely shape to hold and seems fast on water when I gave it a quick run on an old razor.
My suggested approach would be to cut off a section from the thick end, then lap the rest flat. You'll then have two stones from the same grade: one for slurrying and one for the honing. Looking at your picture, you'd still have a very serviceable length one you've made a cut. Of course, the cut off would need lapping also.