Is your feature request related to a problem? Please describe.

I have two WoW accounts under the same Battle.net account, both of which I play on the same computer at home.

When logged into a character on account A, I can't see the inventory of characters on account B (and vice-versa).
This is also true for inventory and guild bank quantities in the tooltip (even if the characters are in the same guild as each other).

Describe the solution you'd like
Consolidation of the inventory/bank/guild bank character data across all local WoW accounts under the same Battle.net account.

I looked into this a little bit to see if/how other addons achieve this and found a lot of posts suggesting using symlinks or TSM (which has its own external executable that consolidates the data). So I am guessing this is otherwise unachievable, but if you could find a way, it would really push Baganator to another level IMO.

So I am guessing this is otherwise unachievable

Not sure about Classic, but at least in Retail you can sync via chat comm. That's also how TSM does it if you have Account Syncing enabled. You can see the communication in the tracer (/etrace) then:

However, if there is a lot of data to sync, this can literally make the game unenjoyable due to permanent stuttering / micro freezes. (By default, it syncs all the time except when in combat. I tweaked my TSM to only sync when a toon is resting, flying, on taxi, etc.; it's fine then).

But if it's just about inventory data (Baganator), I can imagine that the chat comm would hardly be noticeable(?).

TSM (which has its own external executable that consolidates the data)

I think this is only for auction data (not for accounting), but I'm not 100% sure which data is synced via comm and which comes from the auxiliary app.

I'm unsure whether this enhancement is being considered but would like to chime in that I, too, would find it very useful. I've only just started scratching the surface of Baganator but it seems incredibly powerful so far. Syncing across multiple accounts would make it perfect.

I'd also like to comment how useful this feature is and ask for implementation if possible

I totally agree, this would be extremely very useful.

I have a main account with all of my 20+ "normal" toons (plus a few auxiliary AH toons and dedicated bankers), and an AH account with just the main AH toon.

The storage for AH stuff (I mainly sell pets, toys, and such) is spread across several toons on my main account.

I used to run TSM on all toons (including non-AH/non-banker toons), but I stopped because the addon is just too crappy and resource-hungry for that. (I did that only for the inventory sync, because for accounting/logging, Journalator is better anyway.)

When I have both accounts online, it's not a big deal to do a /bgrs search on the main account to see if I have more of whatever my AH toon needs.

But a lot of times I'll just start up the AH account (e.g. while working) to do a quick scan/repost, and then I'm blind: no way to see if I have more of a sold item/pet in stock. I make a note then of what to check next time I log into the main account.

A Syndicator account sync would solve this problem completely. And, as I said, I think the CHAT_MSG_ADDON traffic should be fairly low (compared to what TSM does), since it would just sync inventory numbers (not last year's accounting data including every sold gray item or such).

Blizz did some changes to the inter-addon communication in one of the later DF patches. I have not investigated how this affects (or limits) the communication (TSM sync still seems to work. The respective Ace3 module was updated after that, IIRC).