First off I love Unbounce - and have two suggestions that are inspired by working with Adobe packages and Lucidchart - that might help improve the page builder. They might have been suggested before so apologies if so !
Colour Swatches - I’m sure I’m not the only person who works with either a client’s brand guidelines or with a pre-picked selection of colours. It would be really helpful if we could attach these colours to a master selection area - and then click on them whenever they come into play - whether it be the background, text colour, box colour, buttons etc.
See how objects are placed in proportion to others - Lucidchart does this very well - (I use this to wireframe all my pages for client sign off - before they go to development or building in Unbounce). When you move an object it will bring attention when the space between similar spaced objects is the same - meaning that everything is placed with the right spacing between it - a subtle yet noticeable design strategy that helps achieve the laws of proximity and symmetry.
Hope these might be possible one day.