As much as you can use different grades of alnico to produce different tonal qualities, it actually doesn't make much sense to look at stronger magnets in my opinion. I know lace sensors use Hot barium in some of there models, which has less magnetic pull and higher output. I would say that the best thing to look into in terms of magnets are new grades of metal. I haven't done enough research to know what to look into but if you could say find a new magnet type that has desirable qualities it would be much more suitable for a magnet swap.
In my opinion many people get so caught up in the vintage aspect of magnets that they forget that there are new frontiers to be explored in terms of pickups. Plus as much as certain magnets give off certain qualities, they arent entirely essential to the design of a pickup. Really the magnet functions as the power supply of the pickup and so in many ways new and more efficient materials would be smarter than a different grade of the same material.
I am not discourageing pickup swapping but i think that it would be wise to experiment with materials for a different result.