For all intents and purposes, it is the final major update of Terraria. There won't be a 1.5.
There are a few lose ends that the developers want to tie up in a 1.4.1 update. Examples include the Vanity Contest winners and localization for all the new items that haven't gotten translations in other languages yet. There might also still be some hotfixes in the 1.4.1.x format. But there likely won't be new content after 1.4.1.
I would not expect anything major to come with the 1.4.1 update. At most it will probably be similar in scope to the party update with 1.3.2. A small update that adds a little bit of extra content.
As Rampage also says above, you are still welcome to make suggestions here:
Player Suggestions Select the category that is appropriate for your suggestion and you can create a thread with your idea. Keep in mind it is still very unlikely for suggestions to be implemented, especially at this point where the developers are wrapping things up. If it's something small, it is possible. But I would not expect major new biomes/bosses/npcs or items with brand new mechanics to get added as an example.
There's plenty that many of us wish could still be added to the game, myself included. I have big suggestions of my own from a long time ago. But it is understandable that all developers eventually have to put a finish on a project and move onto the next one. It can't continue forever. Terraria has been lucky to receive 8-9 years of free content which has completely transformed the game from something great into something incredible. Many other developers would have bundled updates such as 1.3 or Journey's End as paid DLC to get more money, and Re-Logic chooses to update the game for free instead. It's a major reason why I have high respect for the company and the people within it.
I understand the feeling of wanting to see a little more added for sure. At the same time, I am also glad Terraria is getting a satisfying conclusion. We don't know for sure what Re-Logic's next game will be, but I am looking forward to seeing what it will be, whether it's Terraria 2 or something else.