I have to admit I’ve only really skimmed this thread, so apologies if I’ve missed something important! However, it seems to me you might be over complicating things a bit… the fact that you’re using micro-inverters gives you some degree of control already. Without any current limiting ( which as mentioned would be needed to truly control the output ) you can simply switch a given battery on or off to give you stepped outputs, so if grid import goes above x you enable one, 2x you enable two, etc.
Given that you’re unlikely not to use the whole capacity of the batteries over a 24hr period, you could also install fixed current limiters between the battery and inverter if you really wanted to, so you get smaller steps ( but longer time on battery. ) This would reduce the efficiency a bit though, both in the inverter and by adding the current limiter.
You might need to seed the inverters to keep them “on” so they remain synced to the grid - that way you can control the output pretty instantly. You could do this from the grid itself I suppose rather than use the batteries ( i.e. feed in a current which is above the inverter power up threshold but below the point where output is generated. ) I’ve not really thought that one through though, so would need some investigation.
Edit: … and thinking about it, just in case you haven’t investigated already… as mentioned above, solar panels are not really voltage sources as such, in fact a solar inverter will normally try to adjust the voltage across the panel to achieve the best power transfer using MPPT, if it tries this with a battery things could go badly wrong depending on how it’s implemented, so having a current limiter in circuit might well be a wise thing anyway.