It would be ideal from a passenger point of view to have entrances on each side of the roads but it would likely be significantly more expensive and the roads with stations are single carriageways (with the possible exception of Clayton) and mainly is shopping strips and thus have lower speed limits.

And to make things even worse – the exits aren’t even on either side of the road!

https://www.danielbowen.com/2016/02/11/skyrail/

I have seen no sign of platform entrances planned for the far end of skyail platforms, they seem to be concentrated.

I would bloody well hope these extended platforms would have multiple exits – it’s a long enough walk already at stations where the exit is at one end!

https://thomasthethinkengine.com/2014/06/18/faster-train-journeys-some-low-hanging-fruit/

The new ‘Skyrail’ stations should be open by 2018, while 10 car trains have to wait until the Metro Tunnel opens in 2026. So empty platforms sitting around for eight years, versus an extended build time while trains are running – it’s a tricky one.

I would assume if the longer trains are going to be running ‘soon’ the platforms should get built now, if it is a decade or more away, maybe give it a miss.

An overseas parallel is the Ma On Shan line in Hong Kong. An elevated railway opened in 2004, 4-car platforms were initially provided but with provision to run far longer trains in future, 8-car trains were introduced in 2017, with platform extensions required

https://en.wikipedia.org/wiki/Ma_On_Shan_Line

It took the MTR four years to complete the work while trains were not running:

https://www.mtr.com.hk/archive/corporate/en/press_release/PR-16-112-E.pdf