YFull estimates TMRCA of I1 as 4600 ybp and TMRCA of U106 as 4800 ybp. Proto-Germanic language is believed to have been spoken to about 2500 ybp, which is much after the development of U106 and I1 subbranches (according to YFull estimations it is more than 2000 years).

If all U106 and I1 is Germanic, then why it is so?

According to Ian McDonald, the sample I7196 from Jinonice in Czech Republic from about 2200 - 1700 BC is U106 > Z2265 > BY30097 > Z381 > Z156 > Z305/Z306/Z307/Z8191 > Z304 > DF98 > S1911 > S1894/S1900. It is from Unetice Culture, which is often associated with Proto-Celtic people. Was I7196 Pre-Proto-Germanic?

What do you think about ethnicity of people with Y-DNA I1 and U106 before the split of Proto-Germanic language? Is it possible that some I1 or U106 people for some time spoke the language which is not Proto-Germanic or its ancestor, but another Indo-European language or maybe even non-IE?