The Microsoft New Console the XBOX Project Scorpio will support XBOX One and XBOX 360 games. It was confirmed by the Lead Engineer of Microsoft Mike Ybarra in Twitter, saying of course XBOX 360 games will work on Scorpio.
— ♏️ike Ybarra (@XboxQwik) November 1, 2016
Also, XBOX Head Phil Spenser is always saying about his ambition to create a gaming ecosystem that will go beyond console generation and also to allow play your games to a number of devices. Albert Penello also added that this should help ease some of the disruption that can happen between console generations.
Microsoft also added backward compatibility on XBOX One in November 2015 as part of their New XBOX experience update. Currently there are 250 games in XBOX 360 that is playable on XBOX One.
Price for XBOX Project Scorpio is not yet available, they should announce it on early 2017.
So, No worries of your old games it will work on XBOX Project Scorpio.