The Nedap Powerrouter has this functionality - indeed, many of the inverters designed for the German market now do this, as the market there is moving away from FIT. The householder wants to use as much self-generated power as possible.
They also do a retrofit model...
The Tesla batteries also aren't hugely revolutionary - alternatives already exist:
A Nedap setup will allow 5KW or 3.7KW peak loads (according to model).
A lot of the cost is tied in to the intelligence of how to handle the charge/discharge, particularly when electricity is charged at different rates at different times (which includes self-generated power). What you really want is something which can determine when you are generating more than you are using, and only store that electricity. The problem with the Nedap solution (in this country) is that the power is stored directly, and doesn't pass through the inverter to go through the generation meter. Thus you don't get your FIT payments until it comes out of your battery. Thus you pay for any inefficiencies.
Mind you, it does open up the possibilities of charging batteries elsewhere and putting them into the system fully charged to then be used and pass through the generation meter at full FIT earning potential. Seems like a lot of effort for a small return...