It depends what you actually want to archive and why. In most cases, multimedia takes up the majority of space, then file attachments and xdc archives, xdc updates, preview HTML message attachments, bot generated messages and then user messages. One can usually trim the fat easily, but only you know which parts are redundant to you personally. For some cases, you can set disappearing messages or deletion of all content locally after a week (or 5) for at least the less important profiles and groups.
Do you honestly intend to keep all of these forever? In general, gmail conditioned most people the bad practice of keeping everything in their mailbox forever (to prepare for future bait & switch and paying for further storage). It is usually more conductive to save and tag only the key information you need in a dedicated personal (family) wiki (or just within DC saved messages or group for the same purpose).
If you are looking for ideas, the following already has potential to solve the use case of the majority of users: