It would seem very difficult to achieve this in practical application.
First of all you'd have to cherry pick the laser diodes to be on the far ends of the normal output wavelength, possibly finding only a percent or so of total production suitable at all. You could perhaps get these as rejects from a manufacturer because they are so far off the intended wavelength, though i doubt that'd be easy.
Then you could use the dichro + PBS approach to combine the beams of 4 into one.
One problem would be cooling though, for something like 25 watts optical output you're looking at 100 watts or so dissipation, not easy to get rid off in anything 'handheld' keeping the temperature low enough to actually hold with without burning your hands.
I wonder what you'd do with a laser that powerful in any case - 5 watts already is a crazy amount of power for a handheld laser. It's obviously enough to blind instantly, but also at the point where it will actually start setting stuff on fire quite quickly. Heck, i have a nasty burn in my wallpaper from just 1 watt, figuring the white wallpaper would reflect enough of it not to char (guessed wrong there).
