well, another doubts that i had some time ago reading unireg source... 

1)why it have a 64k limit? that's a logical limit (a limit in int variable or char or something like it)? or just a "well i think 64k is a good 'constant' limit"?

2)why we "still" with this "old" unireg format? 

i know that someone must start the new format and it will not be compatible with mysql...

but there's any raw idea or a issue in mdev or lauchpad about changing .frm format or creating a new one?

maybe something more human readable YAML or JSON, and a space for engine information https://mariadb.atlassian.net/browse/MDEV-3936