You should also consider the possibility that your potential customer does not have a CC. Here in Germany, that applies to quite a lot of people (sry, I have no numbers).
There's no way I'm going to enter my debit card details for a trial of a product for my employer.
And if we do like the product then the Procurement department will contact you; they don't use credit cards either...
Besides, a free trial might even be incentive enough for someone to get a CC just so they can use your app! I know it was for me when I found something I couldn't pay for otherwise.
Payments are complex and can be extremely localized. This is IMHO not a battle for an early-stage startup to fight. Credit cards are as close as there is to a de facto international standard; go with those to start.
Also -- in my experience, people without CCs reach out and ask for alternate arrangements if they want your service. This is an appropriate time to make sure that e.g. companies that require a complex PO process are spending enough to make it worth your time.
> Starting with an addressable market of 1.5 billion is not a bad thing.
(On the other hand, that means ignoring, what, 3 billion adults? But of course you're right, it's unfeasible to cover every available form of payment)