Why 11 years? A new car model takes about 4-7 years to put into production (depending if it's a derivative model or something completely new, hence the wide range).
Apple started this project back in 2013 (exploration phase) with more people added in 2014 (first poachings, many experts added, see LinkedIn) and now the project is apparently again tripling to close to 2000 people.
It's feasible to create a car within this timeframe, especially given the vast resources Apple has worldwide (both in terms of existing suppliers and financial resources). They could also license a car (BMW i3 rumors) as a technology platform to accelerate the first model launch.
As for contract vs vertically integrated manufacturing, I already discussed this topic here in detail:
Apple developing their own car? - Page 14
I'm much more skeptical of Atieva's and FF's (Faraday Future) EV timeplans, they want to launch their EVs well before Apple's rumored 2019-2020 timeline.
Finally, Apple can and will poach more senior personnel experts thanks to their resources, this will slow down the existing EV/battery competition (as A123 and Tesla already complained about publicly).
I think Tesla investors need to face the fact that the entire PHEV and EV car sector will be very crowded across all models and price ranges by 2018-2020.
In my first post I didn't predict Apple would take 11 years. I said Apple is where Tesla was 11 years ago. I also said that I thought they would take 6-8 years to get to production, which is the high end of the range you quoted for car development. Considering Apple has never built a car and they are intending to produce a very advanced car, I would think the high end of the range is more reasonable. Rather than 2019, I think around 2021 is more likely for Apple, not 2026. I think Tesla will probably have the upper end of the EV market to themselves for the rest of this decade, but I agree the segment will get very crowded, but I don't think it will happen until the early 2020s.