You are probably familiar with crello and canva. Alot of companies use these tools.

If your tool would have keyframes and a bezier editor (like cubic-bezier.com) I would instantly migrate to your tool.

I guess for some customers stock footage is also important - but there you could just partner up with istock etc.

Other things I would hope to see in such a SaaS for marketing motion graphics is: - Motion Blur - gradient with multiple points - basic css styles (dropshadow etc)