You summoned me.
Let's do the math. Let's assume more optimistically 2 cycles per year (charge in spring and fall, discharge summer and winter) for 50 years (100 life cycles), also $8/kWh capex financed at 6%. This amortizes to $0.253/kWh per cycle. The marginal cost would be charging (near $0/kWh), heating for discharge and maintenance, so hopefully all less than $0.05/kWh per cycle. So this system would need to targe discharge opportunities where power prices are above $0.30/kWh. This seems reasonable where you are targeting the most expensive hours of summer and winter, but you've got to have pretty good certainty that you can execute at those peak hours.
BTW if you can do 4 cycles per year overs 25 years, the capex per cycle drops to $0.155/kWh. So it's really advantageous to be able to increase the frequency of cycling, but you run into more challenges around being able to charge for free and finding peak prices to seize on. It depends critically on what other storage and generation assets you're competing against. If high solar and wind penetration assures lots of oversupply hours, then waiting for free power for charging is not a problem. If there is an abundance of storage capacity and backup generators, then finding prices over $0.20/kWh could become tough. For this reason, it tough to anticipate what kind of frequency you'll have 20 to 50 years out. This is true of any sort of battery. So a better approach may be to emphasis high frequency use in the first years to hasten payback and see what the long-term gravy is at potentially lower cycle frequency.
For example, 50 cycles a year (weekly cycling) would amortize at $0.085/kWh. So if a market had a near-term opportunity for weekly peak prices above $0.14/kWh, you could achieve payback within two years. You battery would have little chronological age on it, so you could really test out the cycle life. Managing the fleet might be the key. Each year you add more capacity to your fleet. You dispatch the new batteries more frequently at lower prices and the older ones less frequently at higher prices. Overtime your fleets grows to extract value from the tail distribution of prices.