Microsoft unveiling Windows Phone 10 on Jan 21st 2015?

Microsoft will hold an event in Redmond on January 21st 2015. As Windows 10 for PC continues it's way to next step (Consumer Preview) we might also hear about Windows 10 for phones.

One of my questions is whether Windows Phone 10 will support old Lumia phones. For example there are many used Nokia Lumia 1520 -phones out there waiting for me to pick one. What if Microsoft says Windows Phone 10 is not available for Nokia Lumias? C'mon! There are not that many Windows phones on this planet! They don't exist! So please Microsoft! Make Windows Phone 10 available for at least those Lumias with 1 GB RAM! Check out Lumia 1520 specs here.