[I'm moving this back to gentoo-project only because otherwise the mess gets 
even bigger.]

> What would the tax implications of an umbrella org look like, vs Gentoo
> keeping these in-house?

Well, at the example of SPI (for disclaimer see other mail):

* SPI qualifies as a domestic public charity for purposes of US tax law
* Tax-exempt status under section 501(c)3 of the United States Internal 
Revenue Code was granted on May 23, 1999.
* Donations are tax-deductible in the US

https://www.spi-inc.org/donations/

At the example of the Software Conservancy: 

* Software Freedom Conservancy, Inc. is a 501(c)(3) organization incorporated 
in New York, and donations made to it are fully tax-deductible to the extent 
permitted by law.

https://sfconservancy.org/donate/

Donations to the Gentoo Foundation are not tax-deductible anywhere.

-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)