There are many companies looking to make money out of recycling...

There are many companies looking to make money out of recycling lithium batteries in the years ahead (see NMT just today). So I'm not sure it will be a massive problem.
I'm also not convinced that the preference for lithium as opposed to zinc/bromine for large scale energy storage is just technical. Sure frequency modulation, stabilisation of the system and reducing price scalping were major reasons for the success of Hornsdale but there have been several large solar projects announced in recent times and wherever battery storage is associated, the plan is to use lithium. The Sun Cable project near Tennant Creek puts Hornsdale in the shade for size and scale, has Mike Cannon-Brookes as a key backer (who I assume Simon Hackett would know personally), and intend using Tesla batteries.
Part of the preference may be due to a lack of long term proven performance for zinc/bromine, but I still think cost is the over-riding factor. Money talks loudest. If Redflow could get a cornerstone investor, like an AGL or Energy Australia, to take a 20% placement and then use zinc/bromine batteries in some of their larger battery projects, this would provide credibility and the scale to reduce unit costs.
Time is ticking and with the scale that EV's give to lithium, their unit costs are continuing to fall and widening any gap. Redflow and zinc/bromine need to get moving. I think the Redflow Board knows this and are searching for that cornerstone investor.