It's just not one of the most common uses of aussi in day-to-day spoken French, but it's not dated or even formal. It just depends on how good someone is playing with the grammar. French syntax is very flexible, and the grammatical rules and features exist to accomodate that, but most average speakers (in Québec for sure and even in Europe) stick to the most common forms and won't use inverted structures or conjunctions and such in their rarer accepted uses, but people more used to work with the language will do that. I can think of many instances in which this use of aussi would come very naturally to me. Eg: l'offre prend fin bientôt, aussi je vous conseille de ne pas attendre si vous voulez en profitez / le budget de cette année est très limité, aussi plusieurs coupures sont à prévoir. Ainsi would work well in the second example, not so well for the first.

I actually used aussi that way in a fairly casual email earlier today (... c'est pas mal plus complexe que vous me l'aviez décrit, aussi je voudrais qu'on puisse commencer cette semaine plutôt que etc....)

It's very similar to a use of "thus" in English.

The syntax Castelot used, inverted pronoun and verb with aussi is not the most common, but it's not very rare in written French.