Both the Acer Predator X27 and the similar ASUS ROG Swift PG27UQ have been delayed to 2018. These displays share the AU Optronics M270QAN02.2 AHVA panel, which offers a 3840 x 2160 resolution and 144Hz refresh rate.
The 4K HDR displays from Acer and ASUS promise a feature set unmatched by other displays but it seems the panel isn't ready yet for volume production.
Unfortunately for NVIDIA, this ultimately serves as a de-facto delay for their G-Sync HDR platform, as these displays are the flagship of the line. No other 4K G-Sync HDR displays have been announced, and there are precious few panels set to be released this year that would even meet NVIDIA's needs. Otherwise, in the opposing AMD camp, while none of AMD's partners have announced similar FreeSync displays, any potential products using the AUO panel should be similarly impacted.