Creating PDF/A-2 including JPEG-2000
iText is a PDF library available in Java and C# that allows you to create PDFs that comply to the PDF/A-2 format. You can find some examples here.
Note that you need the core iText library as well as the pdfa library as an addon to the core library. iText core supports JPEG2000 images.
iText is released under the AGPLv3. The AGPL is a free software license, which means that iText is free software. This doesn't mean that you can use iText for free. You can only use iText without purchasing a commercial license if your software is also released under the AGPLv3 (or the GPLv3; you can't release your software under any other license).
None of these obligations or restrictions prevent a viewer that can present a regular PDF (ISO-32000-1) to present a PDF/A document. So in answer to your additional question: any PDF viewer that pretends that it supports ISO-32000-1 automatically also supports ISO-19005-2.
iText is a developer's library. This means that you need to write code to create a PDF document. We have a Java version (iText), a C# version (iTextSharp) and an Android / GAE version (iTextG). There is no GUI (it's a library) and a CLI would be difficult: usually PDFs are created to publish data from a database. How would you connect to a database, perform a query, organize the results of that query through something as simple as a CLI?
Why would we need to combine iText and tiff2pdf? iText supports conversion from TIFF to PDF. Why would we need to combine iText and ImageMagick? iText supports the most common image formats and image manipulation can easily be done through standard Java or C# functionality.
I'm not sure if I understand your question about TIFF. TIFF is a dying format. It is also a pain: the TIFF standard has been interpreted in so many different ways that every one seems to create its own flavor of TIFF. If you look at iText's changelogs, you see that we've been providing fixes to support "dirty" TIFFs in many releases over the last 15 years.
What readers claim they support ISO-32000-1? That's a difficult question. Some may say they support ISO-32000-1, but "forget" that JPEG-2000 is part of that specification.
JPEG-2000 isn't a requirement for PDF/A. As a matter of fact, support for JPEG-2000 was one of the new things that was introduced in PDF/A-2 (it wasn't present in PDF/A-1). You can perfectly create a PDF/A-2 file that doesn't contain a JPEG-2000 image. But maybe I'm misinterpreting your question. You probably meant that viewer who fully support ISO-32000-1 (and ISO-19005-2) are required to support JPEG-2000. That's true and I have no idea which viewers can decode JPEG-2000.