the smiler was a brand new ride type, similarly if I understand the lift hill is a new design to be steeper.
True although it is a refined version of a Eurofighter. The difference between a Eurofighter and an Infinity from Gerstlauer is similar to a Big Dipper and a Stryker with Mack.
Not probably going to happen, Gerstlauer they only had 2 rides (Saw and the smiler) but Mack they have been working with for decades, RMT, TCAAM, battle galleons, etc, and problematic rides happen from time to time, remember Air?
Gerstlauer also they have only built like 5 rides in the UK since the smiler, and none of them to me would have fit in with Gertlauers line up (maybe lego speedway or jumanji)
That is true that Merlin have been working with Mack for years and that will probably go in favour of future rides from Mack.
Air was a prototype which there would be issues. Oblivion and Thirteen are the same.
With Gerstlauer, there was one ride opened in the UK since the Smiler opened which was the SBNO Skyforce at Blackpool. This was from the year of the Smiler Crash and no rides have opened in the UK since the crash from Gerstlauer. The Smiler is the newest UK Gerstlauer coaster.
In the UK, Gerstlauer opened:
Cobra - Paultons - Bobsled - 2006
Troublesome Trucks - Drayton - Junior - 2008
Smiler - Alton Towers - Infinity - 2013
Saw - Thorpe - Eurofighter - 2009
Speed - Oakwood - Eurofighter - 2006
Rage - Adventure Island - Eurofighter - 2007
Skyforce - Blackpool - Sky Fly - 2015
There are plenty of ride types that would fit in at a Merlin park from Gerstlauer however I doubt they're working with Gerstlauer again following the Smiler.
I don't know if the relationship between Merlin and Gerstlauer is something like Cedar Fair where they don't work with certain manufacturers after issues with a coaster or if it's more because they don't have anything that fits their requirements.