a) The exchange virtual-real money WILL get you into a shitload of trouble. Money laundering is the prime issue.

b) Apple and Google are US companies and thus bound by the relatively strict gambling laws in the US - and so your app will not end up in either major app store, only as a sideload for Android.

c) as soon as Real Money is involved, you will attract a massive amount of sharks sucking on the mini fishes, as well as a load of fraudsters, poker-bot users and people trying to game your system (ACH/wire transfer reversals, CC chargebacks, stolen credentials, the list is endless).