While there has been no formal announcement from HK Gaming, the specs of the upcoming Sirius M mouse have leaked on Amazon. Rated at 54g, the mouse uses 20M Omron switches and has approximately dimensions of 121x61x38mm. With a scroll wheel that looks very reminiscent of the Finalmouse Air 58, the size places it right in-between the larger Air 58 and the tiny Ultralight 2. RGB is not present on this model but that might be worth it for the weight reduction.
This is a shape and size that lots of users have been seeking and it looks like HK Gaming will be the first one to deliver this. If QC and build quality of the Sirius holds up, this looks to be one of the more promising lightweight release of late.
Available at Amazon.