Hello, I would like to ask what progress is engine in the Delphi compatibility yet? I have seen in some topic, that it will be focused on after a 7.0 release, and I study in the university, where we want to check Castle Engine and use it in my diploma thesis with Delphi. Also I would like to ask if some futher info can be provided, like maybe just a rough approximation if release will be released in the forseeable future(1-2 months) and how much of code has to be edited to be Delphi compatible, or if there are some known bigger problems in that process etc. Thanks for the answer and any possible info.
For 7.0 release, we still have a number of big-and-small TODOs to make CGE editor really rock. As this is a major feature in CGE 7.0, we want to show its capabilities.
I do not really have a release date yet. A timeline of 4 months seems reasonable. I hope it happens sooner (within 2 months), but I consistently failed when trying to promise too short time 
As for Delphi compatibility work (that follows 7.0 release) – I see no major obstacles, just a lot of “ground work” to make it happen. Base CGE units already work with Delphi ( https://castle-engine.io/supported_compilers.php#section_delphi ), the remaining (big) task is porting the main X3D units and renderer. There isn’t anything particularly troublesome there, CGE is pure modern Pascal code, but it’s just a lot of code We will need to deal in particular with X3DFields (generics being more strict in Delphi, we may need to rework things there) and CastleComponentSerialize (we will need to bring FPC’s FpJson to Delphi).
For sure Delphi compatibility will land in 2021. I hope it will be in 2nd quarter of 2021.