Hi Youssef,
a WYSIWYG editor for SAPUI5 screens is an important feature missing so far. In fact we are currently working on this: It will be a web/cloud based tool enabling drag&drop and support data binding as well. We are now working on a concrete plan for the availability, but the first versions with some limitations (regarding functionality and access) should go out Q2/Q3.
Hope this helps.
Best regards,
Oliver