I imagine this would be very hard to monetize and get customers as-is. The below is merely a brief list of problems that I've thought about

The average user needs to be sold on the effectiveness of a product very fast, on the first usage (or perhaps even sooner!) in order for them to continue using. However, SRS software in general are almost by definition antithetical to that goal: Their benefits do not come until far into the future, worse still it's an undefined time in the future. Sure you can use arguments about the benefits of SRS and the psychology of memory and <insert gwern.net FAQ here>, but it would appear to be an uphill battle to make the benefits immediately relevant and immediately relevant to the people who wouldn't already be using Anki and other free equivalents.

In addition, before you can even start using the product as advertised, you have to learn how to make cards that are easy to memorize or download a deck which is already well made. The first is "Wait so you want me to learn all these tiny rules before I can even start learning? <browser back button>". The second presents a chicken-and-egg problem. How are you going to have high quality decks that teach things? By having users! How are you going to get users? By having high qual- oh, darn.

It would appear that your general idea is going in the right direction; to make the best SRS program as painless as possible and to extend it to be more powerful. Your emphasis though, would appear to be more oriented toward existing power users of SRS. So there's the matter of getting them to switch which... I have no idea how hard that would be. (Sample size of two; you'd obviously build something you'd want to use; I'd jump on board instantly if I could transfer my existing Anki decks).

One possible solution to the adoption is to piggyback it on an existing service; if users get to use it as an additional option on something they already use habitually then getting consistent usage wouldn't be as much of a problem. I believe Khan Academy has expressed interest in including SRS in there. Another is to try and "gamify" it (argh I hate that word) by either making the entire application a sort of game or incorporating cow clicker like features in there to get the user hooked (IT'S NOT EVIL IF THE ADDICTION IS GOOD).

The making your own decks feature can be mostly hidden from the normal user, with a gradual introduction to it as they use the product more (paid feature?). As for having high quality decks; you can try porting the entire Anki library of downloadable decks, filter them in some way and use that to bootstrap up to a much higher standard of quality.

Of course, any and all advice here means absolutely jack compared to the behavior of actual users; release a minimal version, see who bites and check to see what the users complain about before even thinking about what I said here. Making money is and should probably be a distant 4th or 5th consideration behind making a product that you would use and making it easily extensible.