How are you going to handle not very standard
For example, the machine is a member of a FreeIPA or Samba AD or Windows AD domain. Name Switch Service (glibc) plugins
winbind are added to
/etc/nsswitch.conf. When a program calls libc’s functions to get information about users or groups, glibc uses those plugins to prepare an answer. sss NSS plugins interacts with SSS daemon (SSSD), winbind interacts with winbindd (part of samba).
The same situation is with hostnames resolutions. For example, this line from
hosts: files dns myhostname mdns4_minimal
means that when glibc receives a request to resolve a domain name, let it be
xxx.loc, it will first look for a matching record in
/etc/hosts, if it finds nothing, tries DNS resolution which is configured in
/etc/resolv.conf, after that tries to use nss-myhostname, then tries Avahi daemon which implements mDNS/Zeroconf protocol.
Avahi libraries copied from 18.04 will be different than the Avahi daemon running on the host, how will that work? Avahi is a rather simple case, let;s take winbind (Samba). 32 bit winbind and samba libraries will be completely different from the daemon and libraries on the 64 bit host, how will this combination work?
According to this, plus Wine requiring the same runtime in 64 bit and 32 bit modes as @jre-phoenix noticed, plus the necessity to use proprietary drivers for printers and scanners, I would suggest to just build i386 repository as it was always done. Kernel, Chromium, Firefox, Thunderbird, Java etc. should be dropped, because they require many-many resources to test properly and ofthen regress on 32 bit.