The reservoir was only there for mechanical pumps and frame rail high pressure pumps
It held the siphon/prime for mechanical pumps so they would always have a fluid to "pump" to the carb, they don't pump air very well
Any one who has had a dry float bowl and no prime at mechanical pump knows what a pain it can be to re-prime the pump, i.e. get it to suck gas up and over the top of the tank to refill the fuel line to pump, mechanical pumps have good suction with a fluid, but not so much with air
High pressure pumps have no suction, 0, none, nada, with or without fluid
So even with a low pressure pump in the tank a reservoir was needed to "keep the prime" for the high pressure pump in the frame rail so it could instantly provide fuel pressure at injectors, no float bowl with fuel injection, lol
With in tank high pressure pump there can be no loss of Prime assuming you don't run out of gas, lol, so reservoir was removed