In the current group, we haven't really discussed it, but it seems as though we've just sorta naturally fallen into the idea that one attack needs to be made first, then the shield bash, and then whatever...
If pressed to think about it, I'm not really sure where my own individual thinking falls. Thematically, a lot of fighting styles treat the shield as an active weapon, with shoves, bashes, and etc being a prominent part of those styles. So, in my mind, that's one point toward allowing the bonus action to come first. If we're talking strictly rules-as-written, I feel as though the game-logic and how things are labelled seem to point toward things working the way that the group in which I am in currently does things, so that's one mental point toward that. Other rpgs that I play allow a shield be used in a more active manner, but those rpgs also contain combat systems which tend to lean more toward the granularity of a "real" (for a lack of better words) fight; D&D has different assumptions about how the gameworld and combat work, so I'm not quite sure which way that tips my opinion.
From a broader scale, I think that it's hardly the most gamebreaking thing in 5e, but I can see (and have seen) situations in which being able to keep an opponent prone can be quite powerful. Though, even then, we're talking the difference of one attack (attack-bash-attack versus bash-attack-attack), so I am not sure that it really matters or that the feat itself (and being more open to how to rule it) is the problem. I think that, perhaps, it simply highlights one of the areas of the system which arguably has a quirk/flaw on the broader scale of how things are put together, but that manner of construction is relatively consistent with how the rest of the game works.