The problem Fiat will have, if it just wants to sell one or two models at a time, is that the economics of it won't stack up, so while there's some doubts about the different models that could/should or aren't being built, there's also a few things to consider;
1) Fiat has several factories, just in Italy; Mirafiori, Grugliasco (Maser's), Melfi (Jeep/500X), Pomigliano (Panda), and Cassino (Alfa). They need to keep these plants fully occupied.
Sergio closed the works in Termini Imerese (Sicily) in 2011 and that was received hugely negatively in Italy. I remember Sergio was reported as having the hump since he didn't see Fiat as obliged to make cars in Italy at all.. but the reality is, it would be politically difficult to close any more plants. Furthermore, the plants at Mirafiori, Gruliasco, Melfi and Pomigliano have all recently had multi-million Euro upgrades - Cassino was already their most modern plant - so there's no hint of another plant closure.
2) If they can add the Alfa Tonale (Geneva 2019 concept) to Melfi, which already produces the Renegade/500X then there's plenty of capacity there. Pomi' makes only the Panda. That doesn't keep the production machinery particularly "smokin'".
3) Several of the factories have been in and out of Italian slow-time working.. where basically the workers are temporarily laid off (plant closes for a few months). Rationalising its models into the plants above has helped but most plants are borderline low used and could easily add more volume.
4) Sergio managed to buy Chrysler, replace 75% of the range and make a profit from it in just a few years. Sergio also returned Fiat to "no debt" status for the first time since 1976.
Not having a plan to replace "slow selling" models and having no leccy-tech' is possibly one of the consequences of this "diversion" but it seems to me that Fiat is in a reasonable stable place at the moment and just needs to get electrified and also think about what to do with it's most critical models.
Pomigliano needs a "new Panda" (i.e they can't close the plant + they need something to build there = no brainer). Whether they will spin off a sister model remains to be seen.. but Pomi' has huge capacity so with just a single model there they won't exactly have to call in the night shift.
Fiat will also need a new 500 sooner or later. That's built in Poland and shares enough pieces with the Ypsilon that the two are built on the same line. Ypsilon may or may not be replaced (I dunno) but if you have Tychy capable of building both models today, just reducing the model-family to "500-only" must introduce unused capacity.
The random articles about the 120 concept suggest that it can/will form the base of a new Panda and also/possibly the next 500, which together would solve all of Pomigliano's or all of Tychy's problems but would necessarily shift these two models into one plant. What would Tychy build if Panda/500 is at Melfi (or vice-versa)?
So, I suspect Fiat would need to invent a new model, so as to not to close a plant.
It could (if it was me etc.) be tempted to sneak back into the Punto class since it will have a new (adaptable, if they design it right) and modern (hybridisable) chassis ^^ . They would have to differentiate a Punto by making it more premium vs. the traditionally more utilitarian Panda, since they would be closer in size than before... but that means they could (or indeed may need to) spin off supporting models; I have no idea what these could be... but there is clearly scope for a new MiTo or more likely another Ypsilon, since the latter sells well in Italy, if they have a new, more "premium" Punto than they had before.
The main thing to remember with Fiat is that the "5-year plans" seem to represent just a rough idea of some of what the firm wants to do rather than the complete, definitive plan... and that new models can appear from nowhere and also can be introduced in very short order, once the company has set its mind on it.
I'm sure we'll see some surprises from left-field sooner or later. Fiat has been around a long time and it knows how to introduce new models quickly and cheaply... it has cash... and it has plenty of spare capacity. It's almost inevitable that it must bring out a raft of new models, once it has the electric thing sorted..
Ralf S.