This is a summary of things regarding SPI merger that we (the X.Org Board) are pursuing. Links with further information are provided, please peruse them.
X.Org is an Incorp Delaware Non-Stock. X.Org currently has a 501(c)3 tax status in the US, with a board of 8 directors. What the board and the Foundation can do is outlined by our bylaws and limited by our status as 501c3.
Most notable, the board does NOT control the technical direction. It supports the development through sponsoring of conferences and developer programs like GSoC, EVoC, OPW (now Outreachy) etc.
The 501c3 status makes donations tax-deductible in the US. In exchange we have some limits on what we can spend our money on. Conferences and equipment are fine but things like contract work can be problematic. The board has stayed on the safe side, expenses over the last years were almost exclusively conference and related to developer-programs.
Summary: the X.Org Foundation is a US non-profit organization that can take tax-deductible donations and is limited in what the money can be spent on.
Maintaining the 501c3 status requires a number of regular things, e.g. filing taxes (even if there is no income). We have not collected donations for a number of years, certainly since becoming a 501c3. Collecting donations from individual requires infrastructure that we don't currently have (online secure payment systems for example). These rules have caused the Foundation to almost lose the status, even though it was averted and backdated so we have officially continuously maintained the 501c3.
Being an independent 501c3 has non-monetary costs that we struggle to meet. The rules and regulations change and can be tricky to follow. That half the current board is not resident in the US doesn't help.
SPI is an umbrella organisation (and a 501c3 itself) that takes over services for it's associated projects. It legally holds the funds and assets for the project and disperses payments as requested. It provides legal help when needed. The board looked at the SFLC and the Apache Foundation, SPI was the one that was deemed the best fit of the three.
Dissolving the X.Org Foundation as independent 501c3 and joining SPI offloads legal and accounting work to SPI but maintains the workings of the X.Org Foundation in all other means. "SPI does not own, govern or control the associated projects." For example: SPI is the umbrella for Debian, few would argue that this dissolved Debian as a self-governed project. The Foundation was already a 501c3, the limitations on what money may be spent on are thus identical. And SPI grants the freedom to leave at any time.
Summary: Maintaining the 501c3 status is complex, that workload can be moved to SPI by joining. X.Org remains an independent project. Funds and assets will need to be transferred but can be regained if the Foundation leaves SPI.
From a member's POV the most substantial change is that money is dispersed by the SPI treasurer instead of the X.Org treasurer. The board has decided to keep the treasurer position as a gatekeeper, i.e. to tell SPI which requests to honour. Separate accounting will be made for X.Org, ie there will be a separate bank account or at least regular reports of the balance of X.Org's cash.
From the board's POV the most substantial change is that legal and financial matters are handled by SPI without the worry of independently keeping up with and meeting changes in laws and reglations.
From the public's POV the most substantial change is that money may be donated to X.Org through SPI's donation page. SPI keeps 5% of the donation to pay for overhead costs. As a side-effect we also get a share of those donations that go to the general SPI fund (rather than directed at one specific project).
The Foundation has been formally invited to join SPI. Since this would dissolve the 501c3 status and thus require a change in the bylaws, a member vote is required. The vote must meet a two-thirds majority to pass.
Note that the revised bylaws have been extended to not only include the X window system but also Mesa, DRM and Wayland. These projects have been effectively supported by the Foundation anyway, this change makes it more official. The by-laws will be sent out as a separate message.
SPI itself is a 501c3 as well, transferring assets between two 501c3s is fairly straightforward and as mentioned has no effect on how we can spend the money. Based on previous conversations with the SFLC we trust them to handle or help handle the logistics of dismantling our 501c3 status.
Hope that answers most of the questions and provides a clearer picture. If you have any questions left, please let us know.