I have been informed by one member of the SuiteScript team that: “Within the next few releases, although not within one year, we will be disallowing creation of new 1.0 scripts”.

If the above information is accurate, you can expect that before NetSuite version 2019.1, you will need to be writing all of your new scripts in SuiteScript 2.0. Because 1.0 and 2.0 cannot be intermingled in the same script, you may be limited on what you can accomplish or add to your existing 1.0 script. You will not be able to take advantage of the latest features of SuiteScript, and you will be missing out on any continued performance or security improvements that NetSuite makes with SuiteScript 2.0.

I consider delaying a transition to 2.0 extremely risky for any SuiteScript application. Your maintenance efforts will grow exponentially as 1.0 fades into obscurity. You will effectively need to maintain two distinct code bases, and very soon developers who come in to the NetSuite market won't even learn 1.0; thus, there will be even less available talent to help you maintain and improve your applications