[neonrider]

I have got a simple idea how to by using existing default features in X-cart to create something like that where shipping methods would control payment methods somehow, but by using Membership tied to Payment methods. Read on:

In /registered.php replace the languages text label "Sign up for Membership" with the following wording: "Select Delivery method". I know, this is a wrong place for that, but...

Then, at the following page /admin/memberships.php instead of the names for the membership under the drop-down menu enter names of delivery methods such as "UPS", REGISTERED MAIL", "NORMAL MAIL", "INSURED PARCEL", "FEDEX", "PRIORITY", "DHL" etc. etc.

So now when a new customer registers (but only a new customer), they could select shipping method for their future order. I know, that's a weird place to place selection of shipping methods...

Then, under /admin/payment_methods.php creatively apply "Membership" (now replaced with shipping method names) to the Payment Methods there.

I know, the customer will probably still be able to select ANY shipping method down the checkout lane, but now they would be already restricting their own payment methods to what they chose under the "membership/shipping" registration.

Try this and tell us how it went. I will try it too and let you know once and if it works. I know, this is a crazy idea, but its free.