There has been a constant debate to relate To-Dos/Events/Calendar with other entities. This is a very deep area of perusal as there are lots of complications and relations that ought to be handled.
Hence, we will take the divide and build approach here. As of now, whatever is provided, will continue to hold. The newer requests in this particular area will be taken up only post 5.0.0. Till then, in case, there are any one working on those areas, please make contributions in this regard.
vtiger has to grow beyond being a purely tech-lead team. It has to have the balance of tech and the end-user including languages feature. The only way vtiger is going to have a huge circulation is through this approach.