I think it all depends on what happens next year.
If the PS4 has a big year as you predict with ~21 million without a significant price cut then i think LTD numbers has an outside chance of reaching your LTD numbers.
Based on last gen, we saw a sharp decrease in sales once the new platforms came out, so we are not seeing that slow gradual slow down in sales as we did in the PS2 era. So i think your year 4, 5 and 6 estimates are too positive. If Sony releases a PS5 similar to the PS4, in year 5 or 6 then we will see a sharp decrease in sales for PS4. Especially if PS5 has a decent launch price.