I personally try to forecast how many and what kind of Tokyu Corporation's newly-built carriage would introduce.
On January, 2014, carriages seeming to be replaced by the newly-built ones are four sets of 5000 Series on Toyoko Line, two sets of 8590 Series, three of 2000 Series, and two of 8500 Series on Den-en-toshi Line which can't go through Tobu Isesaki and Nikko Lines, and four sets of 8500 Series on Oimachi Line.
Toyoko Line needs three more 8-carriage units to replace four of 5000 Series which temporally transferred from Den-en-toshi Line to compensate for the lack of them to completely replace all old ones before the going-through service to Tokyo Metro Fukutoshin Line. The newly-built ones (5177F, 5178F, and 5179F) and the one introduced in 2013 (5176F) replaces the four 5000 Series.
To Den-en-toshi Line, three 10-carriage (5123F, 5124F, and 5125F) and twelve 6-doored trailers and four motored ones, latter two of which would be coupled with the ones coming back from Toyoko Line to consist of 10-carriage unit, of 5000 Series introduce to replace seven remaining units which can't go through Tobu Railway lines. 8500 Series (8506F and 8542F) and 8590 Series (8594F and 8595F) would be abandoned and 2000 Series (2001F, 2002F and 2003F) would transfer to Oimachi Line.
Since 2009, newly-built carriages of Tokyu Corporation have introduced on Toyoko Line to meet the date for the start of the going-through service to Fukutoshin Line; 5050 and 5050-4000 Series preferentially be built and some 5000 Series, originally made for Den-en-toshi Line, transferred to Toyoko Line.
Though the four sets of 5000 Series on Toyoko Line are adapted to Fukutoshin Line and are treated as the same 8-carriage 5050 Series and Yokohama Minatomirai Railway's Y500 Series, I have expected that these 5000 Series will be replaced because these originally be built for Den-en-toshi Line.
On the other hand, Den-en-toshi Line has had a big problem on train operation to solve; how seven units which can't go through Tobu Railway lines treat since some 5000 Series temporally moved to Toyoko Line.
To solve those problem, the last 8-carriage 5050 Series will be made to replace 5000 Series and to finish the plan of preferential introduction of newly-made carriages.