If you release for x32, you'd have covered the maximum users whereas if you release for x64, you'd have covered only that block. At least open source developers who intend for maximum coverage or user-base for their apps should support at least 32-bit (if not both).

Below is a great answer post in this regard, credits Ken Gregg on Quora[1]:

> Yes, there are a lot of 32-bit programs still being developed/sold/distributed. No, not every program is 64-bit.

> 64-bit operating systems on 64-bit hardware can run 32-bit applications. And there are lots of computers still running 32-bit operating systems (and will for quite some time). So, an application developer can release one 32-bit product and cover the 32-bit and 64-bit customers. Releasing and maintaining two products, one 32-bit and one 64-bit, incurs some costs. And providing only a 64-bit version leaves all the 32-bit customers in the dust. It is logical and cost-effective to supply only a 32-bit version to cover both groups, as long as the application doesn’t require 64-bit features.

> Of course, the embedded systems arena still has tons of new development of 32-bit, 16-bit, and even 8-bit software/firmware. The choice of an embedded microcontroller is based on cost, availability, and features required, so software developed in this realm runs the gamut of bitness.

[1]: https://www.quora.com/Are-32-bit-programs-still-being-made-or-is-every-program-made-nowadays-64-bit/answer/Ken-Gregg