Hello Max,

In, and of itself, there is nothing wrong with your joint selection as presented...

It is much less common (it seems?) in European timber framing modalities compared to Asian systems (going by several names of which I would have to look up as I can't recall them from immediate memory,) and other woodworking crafts of Eastern Europe. I have, as David W. suggested, always read/heard it refereed to in the contemporary parlance of North American timber framing as a:

Diminished Housed Tenon

My concern (perhaps rooted in those same concerns as others have shared thus far?) would be not knowing and/or understanding the application parameters of the entire project?

One principle concern with this form of housed joint (loaded vertically as it is present for floor joists!) correlates directly to the degree of outward thrust it places on the supporting member. Because of the "wedging effect" it has within the given geometry the supporting member has to either be robust enough to withstand this thrust, or have a buttress and/or supporting architecture behind it to withstand these forces. The other, and what seems to be common in historical and/or present versions is a "tying member" in close proximity to the area of this type of joint, thus allowing the tying member to be of less mass as in your case.

Good luck with your project...It sounds fun!!! Let me know if I can expand on anything?

j