I have also been interested in the state of OpenGL of the Intel HD Graphics drivers for a while now and I picked up some information on this along the way.
According to https://mesamatrix.net/ https://mesamatrix.net/ (which visualizes the support of the various OpenGL version/function by Mesa i.e. the 3D driver used on Linux/UNIX) starting with 8th generation graphics hardware (which is used in Broadwell and Airmont according to https://en.wikipedia.org/wiki/Intel_HD_and_Iris_Graphics# Capabilities Intel HD and Iris Graphics - Wikipedia, the free encyclopedia ) there is OpenGL 4.5 support. Mesa doesn't support OpenGL 4.5 yet since that driver is still failing some compliance tests although all necessary functions have been implemented already- according to https://www.phoronix.com/scan.php?page=news_item&px=Intel-Mesa-Collab-GL45-Update Intel Mesa Soon Having OpenGL 4.5, Collabora To Focus On Performance - Phoronix . I am not sure how much of an indication for future OpenGL 4.5 support on Windows this is, given that the Windows driver has supported 4.4 since quite a while and the Mesa one just got support for it just very, very recently. At least it shows, that with recent/current hardware it should be possible to support 4.5.
