What is the best approach to launching a superior system that combines elements of M-Pesa and Alipay?

Chances are your 100+ Million populated country already has a mobile wallet in play or one is about to roll out.

Even if the above is not an issue, what will be of prime importance is whether you would be able to get a no-objection from the regulator and get licensed to roll-out such a service. Invariably every developing country I know of, has regulations that prevent unlicensed operators or service providers to operate any sort of an open-ended payment system with store-value.

Assuming the above two are non-issues for you, here are some points worthy of consideration:

• Distribution Network - You would need access to a very very large distribution network. The distribution layer is what makes all the difference. On-loading/Off-loading of your fiat currency occurs primarily on this layer.
  
• Financial Inclusion - Since you cited developing country, the question that begs to be asked is how many of the adult population is unbanked? If the unbanked figures are huge, you might need to get those figures up (assuming you are not in play with any telco). If you are in play with an MNO, then they would primarily be insisting and setting up their distro network to have more inclusion.
• Wallet Acceptance - Will your wallet acceptance be agnostic or tied to a particular MNO/FI? If latter then you would have to build a very strong case for trade-acceptance of your mobile wallet brand amongst the retail level for the wallet to have any traction.
  
• Transaction Set - Your transaction set should always start from the simplex to the complex. Bill Payments, Utility Bills, Mobile Top-ups, and Peer-to-Peer sending/receiving cash rule the transaction lists almost in any mobile wallet economy that you may look at (barring China, because China is indeed a whole different animal). You can opt for more complex transaction sets, but if you don't cover the very basic sets and are not making a killing, something is serious wrong there.
  
• Escrow on Hold - I would hold on the escrow until such time you have ample of traction on your wallet, and are seeing a strong demand for business related transactions (which inherently on a mobile phone carry risk).
  
• Frictionless - Your entire solution should be frictionless. Lots and lots of testing is required. It should not be assumed what works in Kenya, will easily juxtapose to your economy. It might just backfire! The more open your system, you can bet, the more transactions you will have. Keep it bank agnostic. MNO agnostic. Handset agnostic.