No one has developed a ROM for the a100 since jellybean. Its close relative A500 hasn't had a Rom developed since Lollypop. You have to develop it yourself or find someone to do so. Lineage aka Cyanogenmod won't support the tegra 2. So if anyone developes one it has to be on a Tegra 2 friendly Rom like OmniRom.
Having said that, Rooting accomplishes a lot, in terms of customization, so unless someone develops a New ROM, you can root it.