We went from BaanIV to LN 10.2. It took literally years. But that’s because of us. Migrating from LN 10.2 to LN 10.7 still took a year. We're still using a highly customized installation.
The main problem is, you must migrate the addon programming. So basically, you have to redo every source, you have touched. If you're going to LN 10.7, I strongly advice to switch to extensions. This will be no less time-consuming, but it will make things easier in the future.
Infor will provide standard migrating tools. This will migrate a standard BaanIV installation to LN. But if you want to convert data in a specific way (i.e. converting order numbers) you will have to modify those tools.
In the end we kept the old BaanIV installation as an archive system. Only open orders and basic data has been transferred to LN.
That’s how we did it. On the end users’ side, it’s been a drama, because you can't use the old terminal client anymore. ASCII mode heroes will suffer.