There are various posts concerning methods of safely updating code remotely (via Ethernet, RF links, etc.) where a standalone boot loader is not practical and a fail safe method must be used (optionally with encryption).
The uTasker "Bare-Minimum" loader was developed some 12 years ago to fulfill these requirements and has found reliable use in many Coldfire V2 and Kinetis based products since then.
Its "BM" loader occupies between 2..4k of Flash space (depending on exact configuration), works on (almost) all Kinetis parts and supports uploading to either internal Flash or a number of external SPI connected Flash devices. It can be used also with applications developed with other libraries as long as these can program the uploaded image to the referenced location during normal operation [can be easily inserted at the end of a project development cycle when the necessity for such capability is identified only late in the day].
The code is also available as free Open-Source so can be used even by companies/developers who operate a zero-investment software policy.
If you don't know it yet there is a user's guide at http://www.utasker.com/docs/uTasker/uTasker_BM_Loader.pdf
and a video showing how it can be set up and the configuration/operation verified in the uTasker simulator:
This doesn't replace standalone boot loaders (whereby the uTasker serial loader is also popular for maximum flexibility in Kinetis products: http://www.utasker.com/docs/uTasker/uTaskerSerialLoader.PDF and https://community.nxp.com/thread/317301) but is an alternative, or can be combined with the serial loader (enabling remote updates of the serial loader or the application).
If any questions, just ask them here.