Yea, that's hack job. Although slotting the saddle is an option for guitars with narrow string spacings. I've started selling vintage Yamaha FG saddles with the option of slotting (only $5!) to increase the very narrow 1.97" string spacing to 2.06", 2.09" or 2.125". 2.125" is probably too wide and runs the risk of the E strings rolling off the edges.
That's a great idea, selling pre notched saddles for wider string spacing, why only for vintage Yamaha's, bet there is a market for other makes of guitar too.
The limitation is the width of the end of the fretboard. Whatever that is, that is the maximum you can notch the saddle at. It also depends on how much they beveled the ends of the frets. The customer 1967 FG-150 I'm working on has 1/8" bevels on both ends of the frets!! That's ridiculous!!! I did a complete refret and I can open the string spacing on both ends.