I thing personaly as video technician working on several type of projects that soft edge is very important when having multiple outputs.
i've seen in other discussion that some doesn't see its importance on mapping but in my point ou vue it is.
firstly because for ex. there's a wall of lets say 12m wide and 3m height with 5m distance of projectors using 0.8:1 lens. though the 2 projectors are the same brand and same purchase date everyone working in events knows that the picture won't be of same quality, as 1 of the projectors might have work more than the other or not in the same environment etc. thus one of the two can be little brighter. the only way that when splitting the picture into two that the difference is not obvious is soft edge.
I was very sorry not finding this option in the 1.5 beta version. Hoping to see it in the final version as it would be pointless have multiple projector output and not be able to work with it correctly.
i've tested the mad mapper 1.5 beta with Arkaos GrandVj on my Macbookpro Retina using only 2 outputs out of 3 and tried to use the soft edge in arkaos but doesn't work as this option is only available on output not in syphon.
Please consider this soft edge option else the multi output will be useless for projection.
i think that the best place to put the "soft edge" is to add a new option in the "manage surfaces" section. the new option can work like "mask" thus can soft edge a shape like round or triangle etc that the meeting point of two or more projector are less visible. can do mutiple projection setup ex. 2 VP in front and 1 in the middle in back projection .. thus people can stand infront of screen without have image on them .. it opens possibilities.