It does seem likely that TB4/5 will be another differentiator between the Pro line and the Air line
Maybe for laptops, but the non-Pro Mac mini also has Thunderbolt 4.
They
all have USB4 ports that support 40Gbps, plus many new "Thunderbolt 4" (actually USB 4) features including USB 3.x tunnelling and multi-port downstream USB4 hub support. The ports on a MBA can do anything a TB4 port can do
except support dual external displays.
Since Intel opened up the TB3 spec and USB4 appeared, "Thunderbolt 4" is basically just an additional Intel branding & certification for USB 4 implementations which makes a bunch of optional features from the USB4/USB-C standard optional.
AFAIK The only reason why the M2 MBA and M2 iPad specs say TB3 while the M2 Mac Mini specs say TB4 is that Intel's Thunderbolt 4 branding
requires support for two external displays via Thunderbolt. ...and
that's nothing to do with the TB ports or TB controllers themselves: the M2 SoC can only support two displays total; and whereas the MBA and iPad need one of those for the internal display, the Mini doesn't have an internal display so they're both available over Thunderbolt.
Hence, the M2 Mini gets "Thunderbolt 4" ports while the MBA and iPad get "Thunderbolt/USB 4" ports - and
anything with a M2 Pro or higher processor supports 3 or more displays, so its ports can be called TB4.
The only slight mystery is why the
M3 Airs - which
do support dual external displays if you close the lid - don't now claim TB4, but maybe the "closing the lid" bit doesn't meet Intel's specs or perhaps Apple just aren't bothering since the only
practical upshot would be the words "Thunderbolt 4" in the specs.
Thunderbolt 5 will, presumably, be a similar gold-plating of the USB 4 2.0 80Gbps standard - so any future Mac that still doesn't support two external displays will be "Thunderbolt/USB4 2.0" rather than "Thunderbolt 5".
The fact that the new M4 iPad specs don't mention USB4 2.0 may mean that the M4 series won't be getting TB5 or it may mean they've decided not to support it on the iPad or - given that it's just taken me 6 paragraphs to describe this dumpster fire - they're just keeping their powder dry until they can launch a M5 Pro with Thunderbolt 5 without ifs and buts.