To note; folks are saying that shove as an action is part of the core rules, not that you can convert bonus actions into full actions or vice-versa as standard. You absolutely cannot do that, and for exceptionally good reason.
A bonus action is not just a 'lesser action' and it's definitely not a 'faster action'; they are different types of activity, and are utterly incompatible except in a few very specific cases, which usually come with a cost or require a specific class perk to gain access to. This is part of the system's balance, normally speaking, and freely trading your BAs into actions to allow you to take more BAs is so completely broken and abusable if you scratch even a little way under the surface to look at the implications and results of allowing it.
That said, as others have mentioned, BG3's system barely resembles 5e rules at all, at this stage, and the likelihood of us having a system that isn't balanced entirely around the abuses of Larian's homebrewing, to the negation of all other systems, is minimal, so, in terms of applying that concept to BG3 specifically...
Well, let's look: If everyone can freely use their action to use an additional bonus action, then everyone, of every class, automatically gains the thief rogues' level 3 perk out of the gate. The thief rogue, presumably, keeps theirs and so could theoretically use three bonus actions in a turn, but it would still be heavily devalued as a result.
Our limited movement speed would be devalued as well, since any character with a positive strength score could always jump multiple times in a turn, and use that busted mechanic to cover inordinate amounts of distance beyond their supposed movement limits - something that would further impact upon and cripple the already reduced ranges of ranged caster and archers.
Even for their own system, this would be a bad idea. But, it would stand a chance of making individual characters feel even more pointlessly over-powered and ridiculous, so it's not beyond the realms of possibility that they'll put it in.
