The rumor's legit. I believe that Canon is developing improved 200 and 800.
As to when they will release such lenses is subject to rumor. Consider these past product cycles
20 year cycle
1988 - EF200mm f/1.8L USM
2008 - EF200mm f/2L IS USM
27 year cycle
1981 - New FD800mm f/5.6L (no previous EF predecessor)
2008 - EF800mm f/5.6L IS USM
Will they shorten the product cycle? Possibly, if they can figure a way to increase demand for very specialized lenses.
Before stocks ran the Series I super teles sold for these prices. Included are today's Series II prices.
300
I - $5,000
II - $6,800
400
I - $8,000
II - $11,500
500
I - $7,000
II - $10,500
600
I - $9,200
II - $13,000
A Series II 200 and 800 will be substantially more than $6,000 and $13,900 respectively. Based on the price difference between the actual Series I and II the new 200 and 800 would be priced at the following ranges.
200/2 Series II = $8,160-9,000
800/5.6 Series II = $18,904-20,850
Then again Nikon was able to update their super teles with shorter product cycles without such a severe price increase.
Now to compare Canon vs Nikon as this is the primary incentive to improve products.
200mm f/2.0
Closest Focusing Distance
Canon - 6.2 ft. / 1.9m
Nikon - 6.2 ft. / 1.9m
Filter Size
Canon - 52mm (Drop-in Gelatin Filter Holder)
Nikon - 52mm (Drop-in Gelatin Filter Holder)
Max. Diameter x Length, Weight
Canon - 5.0 in. x 8.2 in./ 128mm x 208mm (maximum lens length); 5.6 lbs./2,520g
Nikon - 4.9 in. x 8.0 in./ 124mm x 203mm (maximum lens length); 6.5 lbs./2,930g
Image Stabilization
Canon - 5-stops
Nikon - 4-stops
800mm f/5.6
Closest Focusing Distance
Canon - 19.7 ft./6.0m
Nikon - Under development since Jul 11, 2012
Filter Size
Canon - 52mm (Drop-in Gelatin Filter Holder)
Nikon - Under development since Jul 11, 2012
Max. Diameter x Length, Weight
Canon - 6.4 in. x 18.1 in./162mm x 461mm (maximum lens length); 9.9 lbs./4,500g
Nikon - Under development since Jul 11, 2012
Image Stabilization
Canon - 4-stops
Nikon - Under development since Jul 11, 2012