Where to embed AppImage magic bytes in the future?

I've been thinking about the magic bytes problem we have with the current type 2 a bit. The only solution is to move these magic bytes to another location. This location must also be at a specific offset and provide enough space for them.

One solution I find especially appealing is the following: AppImage type 1 used ISO9660 whose magic number may be embedded at 3 specific locations: 0x8001, 0x8801, 0x9001. Obviously these locations didn't interfere with the ELF binary. The offsets are (in decimal numbers) around 32-27kiB, our runtime is larger (~150-200kiB). So, the question is, why did ELF and ISO9660 work together in that scenario. And more interestingly, can we just place our own magic bytes where, in case of type 1, the ISO9660 bytes would be expected?