I agree Mike re cost, weight, performance, points of failure and complexity.  Plus as I observed not for the faint hearted.  My suggesting that I haven't ruled the idea out is based on the idea that I never write off a benefit until I know exactly what the costs of intended use are.  For most cruisers, the stability of multis, assuming good seamanship and deployment of drogues (I'm an advocate of the Jordan series dogue) will almost certainly suffice.  For racers, the benefit is clear but the weight penalty is too high.  For thos who might want to venture into the southern oceans where assistance is unlikely and the imposition of costs upon others is significant, I don't know that the idea can be ruled out.  I wonder if anyone on this forum will respond with: well the southern oceans are not for multis.
It is for the above reasons, that I have only ever toyed with the idea.  Empirical supprt for the stability of multis has increased over the years as well.
As to restricting the craft to a round mast: one of the pleasures I hope to gain is having a platform upon which I can toy with inovations and reefable wing rigs (solid leading edge) are amongst them.  We all have differring sets of benefits - the costs are more easy to find common ground on.