Ah yes, we can't afford trams, so let's get more complex tram-trains, which are more expensive than basic trams, and replace the Leeds Supertram system with a tram-train system linking with the national rail network instead! Likely to happen? Erm, if pigs fly, maybe...
And your original post is inaccurate because you said "They are trying something like [Leeds Supertram] on the Penistone line" when in fact they aren't trying anything like that at all. You also admit that you think "[Tram trains are] already being trialled", when it appears to have stalled, this demonstrates that you perhaps don't know a huge amount about the project?
If you think this is realistically going to happen, perhaps you can give your thoughts on the cost of lowering all platforms to 'low floor' height, and if it is deemed unsuccessful, the cost of raising the platforms again? Also, will dedicated platforms be used at Sheffield with low floors and will this not have a negative impact on platforming at Sheffield if one platform is lowered and thus not able to accept normal height trains?
Interesting quote from Ryk Downes, the article doesn't appear to have a date but judging from the URL it is from March. I think he has realised that his quote is rather silly now. Look here
https://www.libdems.org.uk/people/ryk-downes and you will see that he thinks guided trolleybuses could replace Supertram. Unlike tram-trains, a trolleybus system would actually be cheaper than a tram system. So, I think you are quoting old stories and people who have since changed their mind, perhaps?
I'll believe that metro had some crazy idea, sure, but I'm realistic enough to not believe that there will be tram-trains heading off some spur off the viaduct in Leeds into the city centre and then into the suburbs instead of the Supertram project. And also I realise that replacing some Pacers with tram-trains isn't going to make that daft idea any more likely either, and it was just an excuse to make people think it was a good idea. An excuse that appears to have been quietly dropped.