Yes its too long I believe but, as far as BCCI is making money they wont be bothered. However, by the appearance and drop in viewership numbers as quoted by some it looks like the tournament possibly touched its peak in terms of its overall viewership and brand. Any further considerable growth in terms of finances will be mainly dependent upon the growth of the Indian economy and overall money the brands have to invest.
There is a number wise big but overall limited target audience (Based upon number of demographics) to tap in cricketing world in comparison to any other sport like football which is global (In terms of people of different origins and nationalities being into it). Famous leagues in the world with top brand values exist in North American region, some parts of Europe or other similar regions with big economy size and thus much more flexibility to inject money in the sports leagues.
Another thing is that T20 cricket only offers one color of cricket which makes cricket different than quite a few other sports and thus their leagues in that regard. T20 cricket leagues unlike other sporting leagues dont offer the complete dimensions the sport has to offer and in isolation the T20 format even expanding beyond 3-4 weeks becomes a rigorous and monotonous product to watch (Exceptions of some thrillers aside) I believe. In other sports like football the fans generally watch the matches of the sides they are fan of other than maybe some big matches, in cricket the associations with teams despite the branding attempt is not upto the level where a fan only watches the match of his/her team specifically. So IPL possibly have become more like an evening watch in India for most if people dont have much other plans or things to watch (Indian fans can correct me if its wrong understanding).
BCCI needs to balance their play out here, they have increased the teams to 10 which even in other threads I mentioned that they might not have these many quality overseas players or overall player base to keep the competition upto the same level (Arguable as its subjective) but, I think some of the overseas players selected and possibly playing in the league are not upto the quality i.e top international players - most being well known around the globe which was associated with the 8 teams model (Correct me if I am wrong). Further expansion to a bigger window will make the BCCI walk on a thinner line where not only the viewership numbers growth wont be matching the growth the league touched in its peak (Assuming there is growth in numbers as the current years suggestions are showing a decline), there might be few boards and ICC that will try to put their head out of the shell and ask to refrain for the further expansion of window.
So BCCI needs to be careful with their golden goose and try to keep the reality and ambitions as close together as possible.
