Regarding adding new project ideas, I think it is important to clarify the reasoning. As Ksenia wrote, we can accept a limited number of projects due to limited mentoring and org admin capacity. GSoC is normally a competitive environment not only for candidates, but also for projects ideas on their own - there are usually more project ideas than an org can theoretically accept. Of course, early submitted and more established project ideas get a priority. As everywhere in GSoC, it is about the chances of success for the project, and the resulting learnings and value to the community/ecosystem.
Looking at the current list and our project capacity, I would definitely recommend to not add a new project idea at this stage. The reason is simple - most of the candidates, who get accepted, start reviewing the project ideas and contacting the communities early after publishing of the accepted organizations... or even before. So, a late project idea is unlikely to have enough traction and, even so, there is little time for reviewing the proposal and discussing the project plan with the candidate. That makes the late-accepted project ideas much more risky, with much higher failure rates.
In GSoC 2026, I would set a hard deadline for new project ideas - 1 week after the organizations announcements.