Changing to ARM should be easy
The last couple of startups I wrote code for did all their work in Python, NodeJS or Java - it should make no difference going to ARM in x86. If they move services such as RDS / Aurora / whatever, I shouldn't really care about the platform, only the price / performance. Now, if you write C/C++ code and depend on endianness, size of integers, etc, than a) it's most likely poor code, and b) it's your problem. There are exceptions, but experienced coders will define their assumptions and differences in a couple of header files and libraries, then write platform-independent code.
BTW, I code on a Mac, deploy on Linux (several different clouds), as well as deploy Python into Windows for one of my customers. That's a more significant difference than worrying about the CPU architecture.