The biggest reason I have never welded a picatinny rail all the way down to the triple-frame is that I do not like the idea of cutting a notch for charging handle locking clearance. If you omit the lock-back function, you increase the wear on your magazine feed lips and increase malfunction margin by trying to seat the magazine with the bolt closed.
The other concern is the free-floating barrel. If you bob the top of the triple-frame and weld the rails to it, you loose the free-float. I have played with a couple different ideas some of which will be on the run D54P/40's I have planned.
I appreciate the input. It's always good to hear different ideas.