Will there be document capability in the future?

Not alone

Smartsheet is a Data tool that is amazingly adept at allowing the addition of other formats and connecting the text based information. Manipulate and create in the Text format and add from there.

Smartsheet is able to hyper link to Google Docs and that would be the only "editable access". Smartsheet is a Data driven format with amazing functionality.

You have 2 options available - link a editable document via the various linked cloud services so you always have the lates version of the document available, or import your spreadsheet and do all the editing in Smartsheet. There is no need to keep a separate version of a spreadsheet as smartsheet will replace it and can export excel speed sheets or pdf’s as needed

You can add any Word docs or Excel spreadsheets as attachments to your worksheet instead of at a line level. Click the paperclip on the far right side of the screen to open the window for copying attachments. That allows people shared access to your worksheet a quick click spot for shared files. To my knowledge though, it doesn't support simultaneous users so version control can get a little sticky. Another thing that I do is use a cloud space (like a SharePoint Site or OneDrive). I copy the link to the site into my worksheet. My shared users can click the link to take them to the site for the shared documents.