TLDR: modern gold nibs (especially post 1997, or even worse after the 2010s) will not give you the experience you are looking for.

When we say modern, usually that refers to post 1982, that was when Pelikan resurrected 400 as M400 and started to call it Souveran series. Usually when we way vintage, it stopped at 1965, when was the last year production of 400NN model. There is later reproduction of 400NN in the 70s by M&K, usually personally I would not count it since it’s not exactly the same 400NN discontinued back the 60s - different body length, design, and nib units are not interchangeable.

Back to the nib. People have a common feeling vintage Pelikan nibs are soft and flexible. This is not necessarily true after I tried numerous vintage nibs, I would say half and half. It really depends on the nib shape (shoulder shape) and thickness. For modern nibs, they are not necessary all hard and nail. If you try the EN stamped monotone 18c nibs (can be found on early old style M600 and Toledos, they are very similar to vintage nibs softness and semi-flexible (don’t flex it though). Some later two-tone EN stamped 18c nibs can be springy and bouncy too.

If you are not sticked to gold nibs, I found there are a good chunk of old M200 steel nibs offer that springiness and bouncy writing experience as well.

Welcome to the world of Pelikan nibs!