I boot from my SD card, and Deltachat runs fine on it. But this requires a phone that can boot from the SD card. And there is a limit to the size of SD card my phone will take. Continually-bloating proprietary software that forces you to upgrade hardware is common, but not worthy of emulation.
Would it be possible to export your passwords, keys, and contacts, then import them into a fresh DC install, thus shedding the history and storage demands? If so, would it be possible to automate that as a minimal version of the add-second-device process?
Being able to export chats would be a useful adjunct functionality: