Could the Q400 be stretched in any way from a technical standpoint?
Not without reworking the undercarriage again; it's right at the limit of tailstrike risk, 6 degrees of pitch. Which is incidentally the same as the ATR72.
An interesting thought experiment would be a longitudinal splice to widen the fuselage but that has only been done a few times in aviation history and to my knowledge never with a pressurised airframe ( though the 707 was widened from the 367-80, I suppose ).
Yeah but then you will also require more powerful engines to deal with the increased drag and weight and your aircraft becomes more expensive.
The Q400's acquisition price is already in RJ territory, pushing it up further is not an option.
Viking Air is supporting a lot of DHC aircraft, yes and no. Aftermarket support requires maintenance know-how and parts availaibility. Viking is not the only one to have those, operators are rotating spares and MRO's around the world are supporting them.
2. Viking has not sold nor produced many 400 series Twotters since they launched. Some kit aircraft manufacturers are doing better than them. The price tag is too high and the reason why operators keep on going with their old Twotters. Didnt Viking furlough some assembly workers over the summer?
3. The Twotter is the main support product for Viking and the reason why they restarted production of it. But it's not a pressurised aircraft where special repairs need specialised engineering support from the OEM. The SRM is all you need for most repairs.
I think that Viking can do a proper job of supporting the Q400 as can most of the MRO's already working on the Q400's. However when OEM-type engineering support is needed, I'm not sure that they can step up to the plate on this type of aircraft. This is where the big OEM's excell. If you find corrosion or damage that is outside the scope of the SRM, they will tell you how to fix it in no time.
I also doubt that Viking will be able to keep the Q400 production line going. They are struggling with the sales of Twotters, and the Q400 is in a completely different game.
How are they going to win sales campaigns against ATR?