I think the delay of PS6 is likely due to the fact we need to wait more time to have some significant ugprade in tecnologgy to justify a purchase of a new console
I honestly think it should be 2029, but 2029 is too late and the sales would be too dead to justify a 2029 release, so 2028 it is
As for Lifetime sales, at the start of the new generation I thought PS5 would be smaller than PS4 because of rise of PC, but the cost of GPUs became pretty insane. An equivalent to PS5 Pro like a RTX 4070 is costing 650 USD+
I think outselling is PS4 is 90% certainly if they release PS5 in 2028, and 50% certain if they release in 2027