unless something happens with the PS4 like buying the system is proved to cause some STDs then I see no real way that the Switch could ever beat it to 100m.

Seriously? Does this even need to asked?

I'm basing my prediction off all previous nintendo home consoles. SNES, N64, GC, Wii, and Wii U had their successors come out in 5-6 years.

By "fairly quickly", I meant 5-6 years, not 3-4 years. Gen 7-8 have long lifespans for xbox/ps, so compared to that its "fairly quickly".

And just because Nintendo will support Switch for longer than that time period, doesn't mean a new console cant come in the midst of that.

Nice try 

Sony
PS1 --> PS2 (6 years)
PS2 --> PS3 (6 years)
PS3 --> PS4 (7 years)

Microsoft
Xbox -> Xbox 360 (4 years)
Xbox 360 -> Xbox One (8 years)

A system lasting 6 years actually fairly normal. Generation 7 was just prolong so long because the tech wasn't ready and Sony and Microsoft wanted to recoup some of the costs for generation 7. Nintendo home consoles usually last 5 years. The only expectation was the Wii which was replaced in 6 years. Also the Wii was outdated tech wise in 2006 (ignoring motion controls). Nintendo will replace the Switch when it is a good idea and depending on what the competition is doing. If Sony and Microsoft drag out Generation 9 like they are dragging generation 7 & 8 than I wouldn't expect Nintendo to replace the Switch so early. Especially if the Switch is super successful . 

Here are the handhelds
Gameboy -> GBA (11 years!)
GBA -> DS (4 years)
DS -> 3DS (6 years)

Handheld lifetimes are all over the place. The gameboy lasting as long as it did was due to a hardware refresh and pokemon and no competition. GBA had a short lifespan due to Nintendo hurrying up to make a system to compete with the PSP. DS had a standard life cycle and so did the 3DS. Remember the Switch is also a Nintendo handheld. So you have to take consideration of both home and handheld markets. Nintendo might drag out the Switch lifespan if Sony and Microsoft do the same for the PS5 and Xbox 4. I wouldn't be surprised if Nintendo wait 7-8 years to release a new system. I think 6 years is the earliest they will release a Generation 10 console. 

Aligned launch? Anyone's game at this point. I'd prefer to wait for the full first year sales for both platforms before giving an answer, and even then I remain skeptical of giving a solid answer as I'm not sure how frontloaded Switch will be.

As far as who will hit it first, it's a no brainier that 70m+ is closer to 100m than 14m.

I am also interested in seeing what sort of legs Switch will have first, may have a lot of early adopters because of the terrible Wii U experience.

It's a secret ballot. Tag.

The ps4 will surpass 100m early next year and wont hit a brick wall after that. I'm not even sure switch could reach 80m. Switch might barely reach 100m lifetime which means it would take 7-8 years for switch to get to 100m just like the wii

It'll likely be the PS4, though how is the Switch selling compared to the PS4 at the time of its 1st year?

wow lots of people missing launch aligned (or was there an edit)

I voted PS4 but then again if Pokemon ends up being a monster along with Animal Crossing and who knows what else... I think LAUNCH ALIGNED Nintendo is not necessarily out of the running for fastest to 100 mil.