The requirement for a minimum 1.375 tubing is still there:
9.4.5.F.
Exceptions for Formula Cars and Sports Racing cars
Any roll hoop design which does not comply with the specifications in 9.4.5, will only be considered
if it is accompanied by engineering specifications signed by a registered engineer stating that the
design meets the stress loading requirements below. No alternate roll hoop will be considered unless
it contains a main hoop having a minimum tubing size of 1.375” x .080” wall thickness. The roll bar
must be capable of withstanding the following stress loading applied simultaneously to the top of the
roll bar: 1.5 (X) laterally, 5.5 (X) longitudinally in both the fore and aft directions, and 7.5 (X) vertically,
where (X) = the minimum weight of the car.
i would take that to mean in essence that no car will be allowed to use main hoop tubing that is any smaller than the 1.375 x .080 specification.